diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1e5db0907..cd39e05b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,7 +28,7 @@ Versions:
 
 # Upcoming WeKan ® release
 
-This release [fixes](https://github.com/wekan/wekan/commit/357de728c03113b787065bac2c5832ad77f1a117) the following CRITICAL SECURITY ISSUES:
+This release adds the following [CRITICAL SECURITY FIXES](https://github.com/wekan/wekan/commit/357de728c03113b787065bac2c5832ad77f1a117):
 
 - [Fix GHSA-qfqv-42qw-vvwh: `cloneBoard` Meteor method has no authorization check — any user can clone (read) any private board by ID (CWE-639, CWE-862)](https://github.com/wekan/wekan/security/advisories/GHSA-qfqv-42qw-vvwh).
   The `cloneBoard` Meteor method in `models/import.js` copied an entire board —
@@ -128,34 +128,8 @@ and, while auditing that client-side permission checks are also enforced server-
     behind global admin. Now requires global admin.
   Thanks to Claude.
 
-and adds the following updates:
+and, in the same access-control audit, the attachment write API was tightened:
 
-- [Update Windows MongoDB](https://github.com/wekan/wekan/commit/beedf2fefa614018ce7ed499465092e814a050d9).
-  Thanks to xet7.
-- [Update DDP transport and reactivity order for multi-tenant deployment](https://github.com/wekan/wekan/pull/6365).
-  Thanks to italojs.
-- [Updated to Meteor 3.5-rc.1](https://github.com/wekan/wekan/commit/29b3f52e50ea2ee9bfbfb98d3842ce8a9b8e52e3).
-  Thanks to Meteor developers.
-- [Fixed OpenAPI REST API documentation generation](https://github.com/wekan/wekan/commit/c71a97cba20247ce227a288fa74ef23cb3c4c83e),
-  which had been broken
-  since after WeKan v7.93 and only generated docs for the `login`/`register`
-  endpoints (2 operations) instead of the full API. The Meteor 3 migration moved
-  the REST routes from `models/*.js` (`JsonRoutes.add(...)`) into
-  `server/models/*.js` (`WebApp.handlers.get/post/put/delete(...)`) and
-  introduced optional chaining (`?.`) that the `esprima` Python parser cannot
-  read, so `openapi/generate_openapi.py` silently skipped every route file.
-  The generator now understands both routing styles, scans both `models/` and
-  `server/models/`, downlevels modern JS syntax so files parse, handles the
-  `type: Array` SimpleSchema idiom, and `releases/rebuild-docs.sh` works directly
-  with Python 3.12.x (PEP 668). The generated `public/api/wekan.yml` /
-  `wekan.html` now cover the full API again (89 operations / 61 paths).
-  Thanks to Claude.
-- **Documented the attachment / file REST API in the OpenAPI docs** — file
-  upload, download, info, listing a board's files, copy, move and delete (the
-  `/api/attachment/*` endpoints registered via `WebApp.handlers.use()`, which the
-  generator cannot auto-discover) are now documented in `openapi/extra_paths.yml`
-  and injected into the generated docs, including their authentication and
-  permission requirements. Thanks to Claude.
 - **Security: attachment write operations in the REST/DDP API now require board
   write access, not just membership (CWE-862, CWE-639).** Both attachment API
   implementations (`server/routes/attachmentApi.js` HTTP routes and
@@ -167,10 +141,9 @@ and adds the following updates:
   admins still allowed); read operations (download / list / info) keep
   membership-level access. Added security tests in
   `server/lib/tests/attachmentApi.tests.js`. Thanks to Claude.
-- **The attachment copy API now honours the admin "Admin Panel / Attachments"
-  API transfer limits.** Copying an attachment creates a new attachment but
-  skipped the `apiUploadBlocked` / `apiUploadMaxBytes` checks that upload
-  enforces; copy now respects them in both API implementations. Thanks to Claude.
+
+and adds the following new features:
+
 - **SVG image uploads are now sanitized instead of rejected.** Uploaded SVGs
   (attachments and avatars) are cleaned in place in `onAfterUpload` via the new
   `models/lib/sanitizeSvg.js`, which removes JavaScript (`<script>`, inline
@@ -178,26 +151,6 @@ and adds the following updates:
   `<iframe>` / `<object>` / `<embed>` and similar active content) and XML loops
   (`<!DOCTYPE>` / `<!ENTITY>` entity-expansion / XXE constructs and
   `<?xml-stylesheet?>`), so SVG images can be uploaded safely. Thanks to Claude.
-- [Fixed Admin Panel / Attachments / Move Attachment doing nothing / crashing](https://github.com/wekan/wekan/commit/d30803276d6d06db44f65ee1fb583cc11aac8b7b).
-  Several issues in the bulk move:
-  - The GridFS source matcher required `meta.gridFsFileId` to be *absent*, but
-    Meteor-Files always sets it, so selecting "MongoDB Meteor-Files" matched zero
-    files and "nothing happened". The matcher now recognizes real GridFS files
-    (`versions.*.storage === 'gridfs'` or a `meta.gridFsFileId` reference), and a
-    "nothing to move" message is shown when a source is empty instead of silently
-    doing nothing.
-  - Moving files crashed the whole server with
-    `FilesCollection#findOne() not available in server` — `ReactiveCache.getAttachment`
-    used a synchronous `findOne()`; it now uses `findOneAsync()`. The background
-    job is also hardened so a single failing file is skipped instead of crashing
-    the server via an unhandled rejection.
-  - The attachment **copy** API now honours the admin API upload limits (it
-    previously skipped them).
-- **Fixed the "MongoDB Meteor-Files" file-count statistic** in Admin Panel /
-  Attachments, which counted *every* attachment metadata document (so files on
-  the Filesystem were wrongly reported as being in GridFS). It now counts only
-  attachments actually stored in GridFS, consistent with the move tool. Also
-  renamed the mislabeled "Mongo-Files" column to "Meteor-Files". Thanks to Claude.
 - **Unified attachment/avatar storage migration: move any → any.** Admin Panel /
   Attachments / Move Attachment can now move **Attachments, Avatars, or both**,
   from **any source to any destination** across Filesystem, Meteor-Files GridFS,
@@ -218,6 +171,91 @@ and adds the following updates:
   factory now carries its collection (`Attachments` or `Avatars`), so **avatars
   can be stored in Meteor-Files GridFS and cloud**, not only on the filesystem.
   Attachment behavior is unchanged. Thanks to Claude.
+
+and adds the following updates:
+
+- [Update Windows MongoDB](https://github.com/wekan/wekan/commit/beedf2fefa614018ce7ed499465092e814a050d9).
+  Thanks to xet7.
+- [Update DDP transport and reactivity order for multi-tenant deployment](https://github.com/wekan/wekan/pull/6365).
+  Thanks to italojs.
+- [Updated to Meteor 3.5-rc.1](https://github.com/wekan/wekan/commit/29b3f52e50ea2ee9bfbfb98d3842ce8a9b8e52e3).
+  Thanks to Meteor developers.
+- **Documented the attachment / file REST API in the OpenAPI docs** — file
+  upload, download, info, listing a board's files, copy, move and delete (the
+  `/api/attachment/*` endpoints registered via `WebApp.handlers.use()`, which the
+  generator cannot auto-discover) are now documented in `openapi/extra_paths.yml`
+  and injected into the generated docs, including their authentication and
+  permission requirements. Thanks to Claude.
+
+and adds the following fixes:
+
+- **[Fixed upgrade crash]() `An error occurred when creating an index for collection
+  "users": Topology is closed` / `MongoServerSelectionError: Server selection
+  timed out after 30000 ms`.** When WeKan started before MongoDB was reachable
+  and had an elected replica-set primary (common right after an upgrade, while
+  MongoDB replays its WiredTiger journal, or when the app container starts at the
+  same instant as the database), the first index creation threw and Node exited.
+  Now:
+  - **WeKan waits until MongoDB is ready** (reachable, with an elected primary)
+    before it starts, in every launch path: `start-wekan.sh`, `start-wekan.bat`,
+    the Snap (`snap-src/bin/wekan-control`), and the app itself
+    (`server/00waitForMongo.js` / `server/lib/mongoStartup.js`, which blocks the
+    first `Meteor.startup` so it also protects the plain Docker image). The Docker
+    `docker-compose.yml` and `docker-compose-multitenancy.yml` now give `wekandb`
+    a `healthcheck` (primary elected) and the WeKan/tenant services
+    `depends_on: condition: service_healthy`.
+  - **If MongoDB stays unreachable for too long** (default 120s, configurable via
+    `WEKAN_DB_WAIT_TIMEOUT`), a clear English-only message is printed to the
+    Node.js console / `docker logs` / `snap logs` explaining that a database
+    upgrade with `mongodump` (old MongoDB) and `mongorestore --drop` (new
+    MongoDB) may be needed, and reminding that attachments and avatars live
+    on disk under `WRITABLE_PATH` (`files`, `attachments`, `avatars`; on Snap
+    `/var/snap/wekan/common/files`, on Docker the `wekan-files` volume at
+    `/data`) and must be copied too. WeKan keeps retrying after printing it.
+  - **Index creation is now idempotent and crash-safe.** A new `ensureIndex`
+    helper checks the existing indexes and only creates the ones that are
+    missing, and never throws — a single index problem is logged in English
+    instead of taking the whole server down. All startup index creation across
+    the model files was switched to it.
+  Thanks to Claude.
+- [Fixed OpenAPI REST API documentation generation](https://github.com/wekan/wekan/commit/c71a97cba20247ce227a288fa74ef23cb3c4c83e),
+  which had been broken
+  since after WeKan v7.93 and only generated docs for the `login`/`register`
+  endpoints (2 operations) instead of the full API. The Meteor 3 migration moved
+  the REST routes from `models/*.js` (`JsonRoutes.add(...)`) into
+  `server/models/*.js` (`WebApp.handlers.get/post/put/delete(...)`) and
+  introduced optional chaining (`?.`) that the `esprima` Python parser cannot
+  read, so `openapi/generate_openapi.py` silently skipped every route file.
+  The generator now understands both routing styles, scans both `models/` and
+  `server/models/`, downlevels modern JS syntax so files parse, handles the
+  `type: Array` SimpleSchema idiom, and `releases/rebuild-docs.sh` works directly
+  with Python 3.12.x (PEP 668). The generated `public/api/wekan.yml` /
+  `wekan.html` now cover the full API again (89 operations / 61 paths).
+  Thanks to Claude.
+- **The attachment copy API now honours the admin "Admin Panel / Attachments"
+  API transfer limits.** Copying an attachment creates a new attachment but
+  skipped the `apiUploadBlocked` / `apiUploadMaxBytes` checks that upload
+  enforces; copy now respects them in both API implementations. Thanks to Claude.
+- [Fixed Admin Panel / Attachments / Move Attachment doing nothing / crashing](https://github.com/wekan/wekan/commit/d30803276d6d06db44f65ee1fb583cc11aac8b7b).
+  Several issues in the bulk move:
+  - The GridFS source matcher required `meta.gridFsFileId` to be *absent*, but
+    Meteor-Files always sets it, so selecting "MongoDB Meteor-Files" matched zero
+    files and "nothing happened". The matcher now recognizes real GridFS files
+    (`versions.*.storage === 'gridfs'` or a `meta.gridFsFileId` reference), and a
+    "nothing to move" message is shown when a source is empty instead of silently
+    doing nothing.
+  - Moving files crashed the whole server with
+    `FilesCollection#findOne() not available in server` — `ReactiveCache.getAttachment`
+    used a synchronous `findOne()`; it now uses `findOneAsync()`. The background
+    job is also hardened so a single failing file is skipped instead of crashing
+    the server via an unhandled rejection.
+  - The attachment **copy** API now honours the admin API upload limits (it
+    previously skipped them).
+- **Fixed the "MongoDB Meteor-Files" file-count statistic** in Admin Panel /
+  Attachments, which counted *every* attachment metadata document (so files on
+  the Filesystem were wrongly reported as being in GridFS). It now counts only
+  attachments actually stored in GridFS, consistent with the move tool. Also
+  renamed the mislabeled "Mongo-Files" column to "Meteor-Files". Thanks to Claude.
 - **Read legacy CollectionFS attachments and avatars in place** (without
   migrating). The backward-compatibility layer
   (`models/lib/attachmentBackwardCompatibility.js`) was broken — it looked up the
diff --git a/docker-compose-multitenancy.yml b/docker-compose-multitenancy.yml
index 162e1dbe3..e484a104b 100644
--- a/docker-compose-multitenancy.yml
+++ b/docker-compose-multitenancy.yml
@@ -58,6 +58,16 @@ services:
           sleep 2
         done
         wait
+    # Report healthy only once the replica set has an elected primary, so the
+    # tenant apps (depends_on: condition: service_healthy) do not start before
+    # MongoDB is ready and crash with "Topology is closed". start_period gives a
+    # large database time to replay its journal after an upgrade.
+    healthcheck:
+      test: ["CMD", "mongosh", "--host", "127.0.0.1", "--port", "27017", "--quiet", "--eval", "try { quit(rs.status().ok === 1 && db.hello().isWritablePrimary ? 0 : 1) } catch (e) { quit(1) }"]
+      interval: 10s
+      timeout: 10s
+      retries: 30
+      start_period: 60s
     volumes:
       - wekan-db:/data/db
       - wekan-db-dump:/dump
@@ -76,7 +86,8 @@ services:
     restart: always
     network_mode: "host"
     depends_on:
-      - wekandb
+      wekandb:
+        condition: service_healthy
     environment:
       - PORT=8081
       - ROOT_URL=https://tenant1.example.com
@@ -100,7 +111,8 @@ services:
     restart: always
     network_mode: "host"
     depends_on:
-      - wekandb
+      wekandb:
+        condition: service_healthy
     environment:
       - PORT=8082
       - ROOT_URL=https://tenant2.example.com
diff --git a/docker-compose.yml b/docker-compose.yml
index 5db931042..fe4a7ccad 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -258,6 +258,17 @@ services:
       - wekan-tier
     expose:
       - 27017
+    # Healthcheck: report healthy only once the replica set has an elected
+    # primary, so the wekan app (depends_on: condition: service_healthy) does
+    # not start before MongoDB is ready and crash with "Topology is closed".
+    # start_period gives a large database time to replay its journal after an
+    # upgrade before failures are counted.
+    healthcheck:
+      test: ["CMD", "mongosh", "--host", "127.0.0.1", "--port", "27017", "--quiet", "--eval", "try { quit(rs.status().ok === 1 && db.hello().isWritablePrimary ? 0 : 1) } catch (e) { quit(1) }"]
+      interval: 10s
+      timeout: 10s
+      retries: 30
+      start_period: 60s
     volumes:
       - /etc/localtime:/etc/localtime:ro
       - wekan-db:/data/db
@@ -902,7 +913,13 @@ services:
       # Wait spinner to use
       # - WAIT_SPINNER=Bounce
       #---------------------------------------------------------------------
-    #depends_on:
+    # Wait for MongoDB to be healthy (replica-set primary elected) before
+    # starting WeKan, so index creation does not crash with "Topology is closed".
+    # If you use FerretDB instead, comment out the wekandb block below and
+    # uncomment the wekan-ferretdb block.
+    depends_on:
+      wekandb:
+        condition: service_healthy
     #  wekan-migrate:
     #    condition: service_completed_successfully
     #  wekan-ferretdb:
diff --git a/models/attachments.server.js b/models/attachments.server.js
index 82312abfa..6366494cb 100644
--- a/models/attachments.server.js
+++ b/models/attachments.server.js
@@ -15,6 +15,7 @@ import AttachmentStorageSettings from './attachmentStorageSettings';
 import Attachments, { normalizeRemovedFiles } from './attachments';
 import Boards from '/models/boards';
 import { allowIsBoardMember } from '/server/lib/utils';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 // ---------------------------------------------------------------------------
 // Server-only configuration
@@ -396,7 +397,7 @@ Meteor.methods({
 // ---------------------------------------------------------------------------
 
 Meteor.startup(async () => {
-  await Attachments.collection.createIndexAsync({ 'meta.cardId': 1 });
+  await ensureIndex(Attachments, { 'meta.cardId': 1 });
 
   // Ensure standard GridFS index on attachments.chunks for efficient chunk lookups.
   // Without this, queries like find({files_id: ObjectId}) do full collection scans.
diff --git a/server/00waitForMongo.js b/server/00waitForMongo.js
new file mode 100644
index 000000000..e5a400580
--- /dev/null
+++ b/server/00waitForMongo.js
@@ -0,0 +1,16 @@
+import { Meteor } from 'meteor/meteor';
+import { waitForMongoReady } from '/server/lib/mongoStartup';
+
+// ============================================================================
+// MUST be the first server import (see server/imports.js) so this Meteor.startup
+// hook is registered first and therefore runs before any other startup hook
+// that creates indexes (server/models/users.js, collectionBootstrap.js, ...).
+//
+// It blocks startup until MongoDB is reachable with an elected replica-set
+// primary, preventing the "An error occurred when creating an index ...
+// Topology is closed" crash when WeKan starts before MongoDB is ready (common
+// right after an upgrade while MongoDB replays its journal).
+// ============================================================================
+Meteor.startup(async () => {
+  await waitForMongoReady();
+});
diff --git a/server/attachmentMigrationStatus.js b/server/attachmentMigrationStatus.js
index e794fd4f4..3edfa8d1d 100644
--- a/server/attachmentMigrationStatus.js
+++ b/server/attachmentMigrationStatus.js
@@ -1,5 +1,6 @@
 import { Meteor } from 'meteor/meteor';
 import AttachmentMigrationStatus from '/models/attachmentMigrationStatus';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 // Allow/Deny rules
 // This collection is server-only and should not be modified by clients
@@ -12,7 +13,7 @@ AttachmentMigrationStatus.allow({
 
 // Create indexes for better query performance
 Meteor.startup(() => {
-  AttachmentMigrationStatus._collection.createIndexAsync({ boardId: 1 });
-  AttachmentMigrationStatus._collection.createIndexAsync({ userId: 1, boardId: 1 });
-  AttachmentMigrationStatus._collection.createIndexAsync({ updatedAt: -1 });
+  ensureIndex(AttachmentMigrationStatus, { boardId: 1 });
+  ensureIndex(AttachmentMigrationStatus, { userId: 1, boardId: 1 });
+  ensureIndex(AttachmentMigrationStatus, { updatedAt: -1 });
 });
diff --git a/server/cronJobStorage.js b/server/cronJobStorage.js
index f9b2a73dd..1d29be485 100644
--- a/server/cronJobStorage.js
+++ b/server/cronJobStorage.js
@@ -6,6 +6,7 @@
 import { Meteor } from 'meteor/meteor';
 import { Mongo } from 'meteor/mongo';
 import CronJobStatus from '/models/cronJobStatus';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 // Collections for persistent storage
 export { CronJobStatus };
@@ -49,26 +50,26 @@ if (Meteor.isServer) {
 if (Meteor.isServer) {
   Meteor.startup(async () => {
     // Index for job status queries
-    await CronJobStatus._collection.createIndexAsync({ jobId: 1 });
-    await CronJobStatus._collection.createIndexAsync({ status: 1 });
-    await CronJobStatus._collection.createIndexAsync({ createdAt: 1 });
-    await CronJobStatus._collection.createIndexAsync({ updatedAt: 1 });
+    await ensureIndex(CronJobStatus, { jobId: 1 });
+    await ensureIndex(CronJobStatus, { status: 1 });
+    await ensureIndex(CronJobStatus, { createdAt: 1 });
+    await ensureIndex(CronJobStatus, { updatedAt: 1 });
 
     // Index for job steps queries
-    await CronJobSteps._collection.createIndexAsync({ jobId: 1 });
-    await CronJobSteps._collection.createIndexAsync({ stepIndex: 1 });
-    await CronJobSteps._collection.createIndexAsync({ status: 1 });
+    await ensureIndex(CronJobSteps, { jobId: 1 });
+    await ensureIndex(CronJobSteps, { stepIndex: 1 });
+    await ensureIndex(CronJobSteps, { status: 1 });
 
     // Index for job queue queries
-    await CronJobQueue._collection.createIndexAsync({ priority: 1, createdAt: 1 });
-    await CronJobQueue._collection.createIndexAsync({ status: 1 });
-    await CronJobQueue._collection.createIndexAsync({ jobType: 1 });
+    await ensureIndex(CronJobQueue, { priority: 1, createdAt: 1 });
+    await ensureIndex(CronJobQueue, { status: 1 });
+    await ensureIndex(CronJobQueue, { jobType: 1 });
 
     // Index for job errors queries
-    await CronJobErrors._collection.createIndexAsync({ jobId: 1, createdAt: -1 });
-    await CronJobErrors._collection.createIndexAsync({ stepId: 1 });
-    await CronJobErrors._collection.createIndexAsync({ severity: 1 });
-    await CronJobErrors._collection.createIndexAsync({ createdAt: -1 });
+    await ensureIndex(CronJobErrors, { jobId: 1, createdAt: -1 });
+    await ensureIndex(CronJobErrors, { stepId: 1 });
+    await ensureIndex(CronJobErrors, { severity: 1 });
+    await ensureIndex(CronJobErrors, { createdAt: -1 });
   });
 }
 
diff --git a/server/imports.js b/server/imports.js
index 6400e5994..616da2a28 100644
--- a/server/imports.js
+++ b/server/imports.js
@@ -3,6 +3,11 @@
 // Loaded by server/main.js after bootstrap (collectionHelpers) completes.
 // ============================================================================
 
+// ****IMPORTANT**** Wait for MongoDB to be ready BEFORE anything else, so the
+// first index creation never crashes the server with "Topology is closed".
+// Registers the first Meteor.startup hook, so it runs before index-creating ones.
+import '/server/00waitForMongo';
+
 // ****IMPORTANT**** Initialize upload directories BEFORE models are loaded
 // This ensures ostrio:files can create necessary directories without permission errors
 import '/server/initializeDirs';
diff --git a/server/lib/mongoStartup.js b/server/lib/mongoStartup.js
new file mode 100644
index 000000000..289e51eeb
--- /dev/null
+++ b/server/lib/mongoStartup.js
@@ -0,0 +1,172 @@
+import { MongoInternals } from 'meteor/mongo';
+
+// ============================================================================
+// WeKan MongoDB startup helpers
+//
+// Two problems this module solves, both seen when upgrading WeKan/MongoDB
+// (e.g. the "Topology is closed" / "Server selection timed out" crash on
+// startup, https://github.com/wekan/wekan/issues ):
+//
+//   1. WeKan must WAIT until MongoDB is actually reachable and has an elected
+//      replica-set primary before it starts creating indexes. Otherwise the
+//      first createIndex() throws and Node exits.
+//
+//   2. Index creation must be IDEMPOTENT: check the existing indexes and only
+//      add the ones that are missing, so an upgrade never crashes on an index
+//      that already exists (or has different options).
+//
+// All log messages here are intentionally English only (no i18n) so they are
+// readable in `docker logs`, `snap logs wekan` and the Node.js terminal.
+// ============================================================================
+
+// How long to wait for MongoDB before printing the "you may need to upgrade
+// the database with mongodump/mongorestore" guidance. We keep retrying after
+// this; we just stop staying silent. Override with WEKAN_DB_WAIT_TIMEOUT
+// (seconds).
+const WAIT_HINT_AFTER_SECONDS = parseInt(
+  process.env.WEKAN_DB_WAIT_TIMEOUT || '120',
+  10,
+);
+const RETRY_INTERVAL_MS = 5000;
+
+// Printed once, in English only, when MongoDB stays unreachable long enough
+// that a database/MongoDB-version upgrade is the likely cause.
+const UPGRADE_HINT = `
+========================================================================
+WeKan: still cannot connect to MongoDB.
+
+If you just upgraded WeKan or MongoDB, the existing database may have been
+created by an OLDER MongoDB version that the new MongoDB cannot open, so
+MongoDB never finishes starting and WeKan keeps waiting here.
+
+How to upgrade the database (dump with the old version, restore with the new):
+
+  1. Start the OLD, previously-working MongoDB version.
+  2. Back up:    mongodump --archive=/dump/wekan.archive --gzip
+  3. Stop the old MongoDB. Start the NEW MongoDB version on an EMPTY data dir.
+  4. Restore:    mongorestore --archive=/dump/wekan.archive --gzip --drop
+  5. Start WeKan again.
+
+Attachments and avatars are stored ON DISK under WRITABLE_PATH, NOT in
+MongoDB, so when moving to a new server ALSO copy that whole directory
+(it contains "files", "attachments" and "avatars"):
+  - Snap:   /var/snap/wekan/common/files
+  - Docker: the "wekan-files" volume mounted at /data
+  - Source: the WRITABLE_PATH you configured in start-wekan.sh
+
+Also check the MongoDB logs (docker logs wekan-db / snap logs wekan.mongodb)
+for the real reason, for example:
+  - incompatible featureCompatibilityVersion (step major versions one by one),
+  - "wrong mongod version" on the data files,
+  - an unclean shutdown that needs  mongod --repair.
+WeKan will keep retrying every ${RETRY_INTERVAL_MS / 1000}s in case MongoDB is
+just slow to replay its journal.
+========================================================================
+`;
+
+function getRawDb() {
+  // Available once the `mongo` package has loaded, which is before any
+  // application code runs.
+  return MongoInternals.defaultRemoteCollectionDriver().mongo.db;
+}
+
+// Resolve a node-mongodb rawCollection from a Meteor Mongo.Collection, a
+// Meteor-Files FilesCollection (its Mongo.Collection is at `.collection`), or
+// anything that already exposes rawCollection().
+function getRawCollection(collection) {
+  if (!collection) return null;
+  if (typeof collection.rawCollection === 'function') {
+    return collection.rawCollection();
+  }
+  if (collection._collection && typeof collection._collection.rawCollection === 'function') {
+    return collection._collection.rawCollection();
+  }
+  if (collection.collection && typeof collection.collection.rawCollection === 'function') {
+    return collection.collection.rawCollection();
+  }
+  return null;
+}
+
+// One connectivity probe: must answer AND be a writable primary, because we
+// are about to create indexes (a write). Throws on any failure.
+async function probeMongo() {
+  const hello = await getRawDb().command({ hello: 1 });
+  if (!hello.isWritablePrimary) {
+    throw new Error('MongoDB reachable but replica-set primary not elected yet');
+  }
+}
+
+/**
+ * Block until MongoDB is reachable and a writable primary is available.
+ * Never rejects: it keeps retrying, and after WAIT_HINT_AFTER_SECONDS it prints
+ * the (English) mongodump/mongorestore upgrade guidance once.
+ */
+export async function waitForMongoReady() {
+  let waited = 0;
+  let hintShown = false;
+  // Fast path: already connected.
+  try {
+    await probeMongo();
+    return;
+  } catch (e) {
+    console.log(`WeKan: waiting for MongoDB to become ready (${e.message})...`);
+  }
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    await new Promise(resolve => setTimeout(resolve, RETRY_INTERVAL_MS));
+    waited += RETRY_INTERVAL_MS / 1000;
+    try {
+      await probeMongo();
+      console.log('WeKan: MongoDB is ready.');
+      return;
+    } catch (e) {
+      if (!hintShown && waited >= WAIT_HINT_AFTER_SECONDS) {
+        console.error(UPGRADE_HINT);
+        hintShown = true;
+      } else {
+        console.log(`WeKan: MongoDB not ready yet (${e.message}), retrying in ${RETRY_INTERVAL_MS / 1000}s...`);
+      }
+    }
+  }
+}
+
+/**
+ * Idempotent index creation: look at the indexes that already exist on the
+ * collection and only create the index when no index with the same key pattern
+ * is present. Never throws — a single index problem must not crash startup.
+ *
+ * @param {Mongo.Collection|{rawCollection:Function}} collection
+ * @param {Object} keys     index key spec, e.g. { boardId: 1 }
+ * @param {Object} [options] passed straight through to createIndex (unique, etc.)
+ * @returns {Promise<boolean>} true if an index was created, false if skipped
+ */
+export async function ensureIndex(collection, keys, options = {}) {
+  const raw = getRawCollection(collection);
+  if (!raw) {
+    console.error('WeKan ensureIndex: could not resolve rawCollection, skipping', keys);
+    return false;
+  }
+  const wanted = JSON.stringify(keys);
+  try {
+    let existing = [];
+    try {
+      existing = await raw.indexes();
+    } catch (e) {
+      // Collection may not exist yet — that is fine, createIndex will make it.
+      existing = [];
+    }
+    const alreadyThere = existing.some(idx => JSON.stringify(idx.key) === wanted);
+    if (alreadyThere) {
+      return false;
+    }
+    await raw.createIndex(keys, options);
+    return true;
+  } catch (e) {
+    // e.g. transient connection error or an option conflict on an existing
+    // index. Log in English and continue; do not crash the whole server.
+    console.error(
+      `WeKan ensureIndex: failed to ensure index ${wanted} on "${raw.collectionName}": ${e.message}`,
+    );
+    return false;
+  }
+}
diff --git a/server/models/actions.js b/server/models/actions.js
index 8e7e90e2e..ec92f32aa 100644
--- a/server/models/actions.js
+++ b/server/models/actions.js
@@ -1,6 +1,7 @@
 import { Meteor } from 'meteor/meteor';
 import Actions from '/models/actions';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.startup(async () => {
-  await Actions._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Actions, { modifiedAt: -1 });
 });
diff --git a/server/models/activities.js b/server/models/activities.js
index 6a82203f8..2ebe3a00a 100644
--- a/server/models/activities.js
+++ b/server/models/activities.js
@@ -7,6 +7,7 @@ import Cards from '/models/cards';
 import Integrations from '/models/integrations';
 import { RulesHelper } from '/server/rulesHelper';
 import { Notifications } from '/server/notifications/notifications';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 function normalizeActivityText(value, fallback = '') {
   return typeof value === 'string' ? value : fallback;
@@ -32,20 +33,20 @@ Activities.after.insert(async (userId, doc) => {
 });
 
 Meteor.startup(async () => {
-  await Activities._collection.createIndexAsync({ createdAt: -1 });
-  await Activities._collection.createIndexAsync({ modifiedAt: -1 });
-  await Activities._collection.createIndexAsync({ updatedAt: 1, deleted: 1 });
-  await Activities._collection.createIndexAsync({ cardId: 1, createdAt: -1 });
-  await Activities._collection.createIndexAsync({ boardId: 1, createdAt: -1 });
-  await Activities._collection.createIndexAsync(
+  await ensureIndex(Activities, { createdAt: -1 });
+  await ensureIndex(Activities, { modifiedAt: -1 });
+  await ensureIndex(Activities, { updatedAt: 1, deleted: 1 });
+  await ensureIndex(Activities, { cardId: 1, createdAt: -1 });
+  await ensureIndex(Activities, { boardId: 1, createdAt: -1 });
+  await ensureIndex(Activities, 
     { commentId: 1 },
     { partialFilterExpression: { commentId: { $exists: true } } },
   );
-  await Activities._collection.createIndexAsync(
+  await ensureIndex(Activities, 
     { attachmentId: 1 },
     { partialFilterExpression: { attachmentId: { $exists: true } } },
   );
-  await Activities._collection.createIndexAsync(
+  await ensureIndex(Activities, 
     { customFieldId: 1 },
     { partialFilterExpression: { customFieldId: { $exists: true } } },
   );
diff --git a/server/models/boards.js b/server/models/boards.js
index 4b235448c..c8d50935b 100644
--- a/server/models/boards.js
+++ b/server/models/boards.js
@@ -16,6 +16,7 @@ import Swimlanes from '/models/swimlanes';
 import TableVisibilityModeSettings from '/models/tableVisibilityModeSettings';
 import Triggers from '/models/triggers';
 import Users from '/models/users';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 const getTAPi18n = () => require('/imports/i18n').TAPi18n;
 
@@ -327,15 +328,15 @@ Boards.before.insert(async (userId, doc) => {
 });
 
 Meteor.startup(async () => {
-  await Boards._collection.createIndexAsync({ modifiedAt: -1 });
-  await Boards._collection.createIndexAsync(
+  await ensureIndex(Boards, { modifiedAt: -1 });
+  await ensureIndex(Boards, 
     {
       _id: 1,
       'members.userId': 1,
     },
     { unique: true },
   );
-  await Boards._collection.createIndexAsync({ 'members.userId': 1 });
+  await ensureIndex(Boards, { 'members.userId': 1 });
 });
 
 Boards.after.insert(async (userId, doc) => {
diff --git a/server/models/cardComments.js b/server/models/cardComments.js
index 1930ca1eb..47c4f4bf0 100644
--- a/server/models/cardComments.js
+++ b/server/models/cardComments.js
@@ -5,6 +5,7 @@ import { sendJsonResult } from '/server/apiMiddleware';
 import { ReactiveCache } from '/imports/reactiveCache';
 import Activities from '/models/activities';
 import CardComments from '/models/cardComments';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 async function commentCreation(userId, doc) {
   const card = await ReactiveCache.getCard(doc.cardId);
@@ -24,8 +25,8 @@ async function commentCreation(userId, doc) {
 }
 
 Meteor.startup(async () => {
-  await CardComments._collection.createIndexAsync({ modifiedAt: -1 });
-  await CardComments._collection.createIndexAsync({ cardId: 1, createdAt: -1 });
+  await ensureIndex(CardComments, { modifiedAt: -1 });
+  await ensureIndex(CardComments, { cardId: 1, createdAt: -1 });
 });
 
 CardComments.after.insert(async (userId, doc) => {
diff --git a/server/models/cards.js b/server/models/cards.js
index f1d33f64e..6b4fe0fe0 100644
--- a/server/models/cards.js
+++ b/server/models/cards.js
@@ -21,6 +21,7 @@ import Cards, {
   updateActivities,
 } from '/models/cards';
 import Lists from '/models/lists';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.methods({
   async createCardWithDueDate(boardId, listId, title, dueDate, swimlaneId) {
@@ -399,11 +400,11 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Cards._collection.createIndexAsync({ modifiedAt: -1 });
-  await Cards._collection.createIndexAsync({ updatedAt: 1, deleted: 1 });
-  await Cards._collection.createIndexAsync({ boardId: 1, createdAt: -1 });
-  await Cards._collection.createIndexAsync({ boardId: 1, listId: 1 });
-  await Cards._collection.createIndexAsync({ parentId: 1 });
+  await ensureIndex(Cards, { modifiedAt: -1 });
+  await ensureIndex(Cards, { updatedAt: 1, deleted: 1 });
+  await ensureIndex(Cards, { boardId: 1, createdAt: -1 });
+  await ensureIndex(Cards, { boardId: 1, listId: 1 });
+  await ensureIndex(Cards, { parentId: 1 });
   Meteor.defer(() => {
     addCronJob();
   });
diff --git a/server/models/checklistItems.js b/server/models/checklistItems.js
index 4ed4f33ee..9e893a731 100644
--- a/server/models/checklistItems.js
+++ b/server/models/checklistItems.js
@@ -11,12 +11,13 @@ import ChecklistItems, {
   publishChekListUncompleted,
 } from '/models/checklistItems';
 import Activities from '/models/activities';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.startup(async () => {
-  await ChecklistItems._collection.createIndexAsync({ modifiedAt: -1 });
-  await ChecklistItems._collection.createIndexAsync({ updatedAt: 1, deleted: 1 });
-  await ChecklistItems._collection.createIndexAsync({ checklistId: 1 });
-  await ChecklistItems._collection.createIndexAsync({ cardId: 1 });
+  await ensureIndex(ChecklistItems, { modifiedAt: -1 });
+  await ensureIndex(ChecklistItems, { updatedAt: 1, deleted: 1 });
+  await ensureIndex(ChecklistItems, { checklistId: 1 });
+  await ensureIndex(ChecklistItems, { cardId: 1 });
 });
 
 ChecklistItems.after.update(async (userId, doc, fieldNames) => {
diff --git a/server/models/checklists.js b/server/models/checklists.js
index 712053e82..f88e43a6e 100644
--- a/server/models/checklists.js
+++ b/server/models/checklists.js
@@ -7,6 +7,7 @@ import { allowIsBoardMemberByCard } from '/server/lib/utils';
 import Checklists from '/models/checklists';
 import ChecklistItems from '/models/checklistItems';
 import Activities from '/models/activities';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.methods({
   async moveChecklist(checklistId, newCardId) {
@@ -66,8 +67,8 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Checklists._collection.createIndexAsync({ modifiedAt: -1 });
-  await Checklists._collection.createIndexAsync({ cardId: 1, createdAt: 1 });
+  await ensureIndex(Checklists, { modifiedAt: -1 });
+  await ensureIndex(Checklists, { cardId: 1, createdAt: 1 });
 });
 
 Checklists.after.insert(async (userId, doc) => {
diff --git a/server/models/collectionBootstrap.js b/server/models/collectionBootstrap.js
index 82f609178..24d42df70 100644
--- a/server/models/collectionBootstrap.js
+++ b/server/models/collectionBootstrap.js
@@ -16,14 +16,15 @@ import InviteToBoardRolesSettings, {
 } from '/models/inviteToBoardRolesSettings';
 import Triggers from '/models/triggers';
 import UnsavedEditCollection from '/models/unsavedEdits';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.startup(async () => {
-  await AccessibilitySettings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(AccessibilitySettings, { modifiedAt: -1 });
   if (!(await AccessibilitySettings.findOneAsync({}))) {
     await AccessibilitySettings.insertAsync({ enabled: false, sort: 0 });
   }
 
-  await AccountSettings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(AccountSettings, { modifiedAt: -1 });
   await AccountSettings.upsertAsync(
     { _id: 'accounts-allowEmailChange' },
     { $setOnInsert: { booleanValue: false, sort: 0 } },
@@ -37,18 +38,19 @@ Meteor.startup(async () => {
     { $setOnInsert: { booleanValue: false, sort: 0 } },
   );
 
-  await Announcements._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Announcements, { modifiedAt: -1 });
   if (!(await Announcements.findOneAsync({}))) {
     await Announcements.insertAsync({ enabled: false, sort: 0 });
   }
 
-  await CardCommentReactions._collection.createIndexAsync(
+  await ensureIndex(
+    CardCommentReactions,
     { cardCommentId: 1 },
     { unique: true },
   );
-  await InvitationCodes._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(InvitationCodes, { modifiedAt: -1 });
 
-  await LockoutSettings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(LockoutSettings, { modifiedAt: -1 });
   await LockoutSettings.upsertAsync(
     { _id: 'known-failuresBeforeLockout' },
     {
@@ -117,31 +119,31 @@ Meteor.startup(async () => {
     },
   );
 
-  await OrgUser._collection.createIndexAsync({ orgId: -1 });
-  await OrgUser._collection.createIndexAsync({ orgId: -1, userId: -1 });
+  await ensureIndex(OrgUser, { orgId: -1 });
+  await ensureIndex(OrgUser, { orgId: -1, userId: -1 });
 
-  await Presences._collection.createIndexAsync({ serverId: -1 });
+  await ensureIndex(Presences, { serverId: -1 });
 
-  await PositionHistory._collection.createIndexAsync({ boardId: 1, entityType: 1, entityId: 1 });
-  await PositionHistory._collection.createIndexAsync({ boardId: 1, entityType: 1 });
-  await PositionHistory._collection.createIndexAsync({ createdAt: -1 });
+  await ensureIndex(PositionHistory, { boardId: 1, entityType: 1, entityId: 1 });
+  await ensureIndex(PositionHistory, { boardId: 1, entityType: 1 });
+  await ensureIndex(PositionHistory, { createdAt: -1 });
 
-  await Rules._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Rules, { modifiedAt: -1 });
 
-  await TableVisibilityModeSettings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(TableVisibilityModeSettings, { modifiedAt: -1 });
   await TableVisibilityModeSettings.upsertAsync(
     { _id: 'tableVisibilityMode-allowPrivateOnly' },
     { $setOnInsert: { booleanValue: false, sort: 0 } },
   );
 
-  await InviteToBoardRolesSettings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(InviteToBoardRolesSettings, { modifiedAt: -1 });
   await InviteToBoardRolesSettings.upsertAsync(
     { _id: INVITE_TO_BOARD_ROLES_ID },
     { $setOnInsert: { allowedRoles: INVITE_TO_BOARD_ROLES_DEFAULT, sort: 0 } },
   );
 
-  await Triggers._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Triggers, { modifiedAt: -1 });
 
-  await UnsavedEditCollection._collection.createIndexAsync({ modifiedAt: -1 });
-  await UnsavedEditCollection._collection.createIndexAsync({ userId: 1 });
+  await ensureIndex(UnsavedEditCollection, { modifiedAt: -1 });
+  await ensureIndex(UnsavedEditCollection, { userId: 1 });
 });
diff --git a/server/models/customFields.js b/server/models/customFields.js
index 869ef509d..68116ea62 100644
--- a/server/models/customFields.js
+++ b/server/models/customFields.js
@@ -7,6 +7,7 @@ import { ReactiveCache } from '/imports/reactiveCache';
 import Activities from '/models/activities';
 import Cards from '/models/cards';
 import CustomFields from '/models/customFields';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 async function customFieldCreation(userId, doc) {
   await Activities.insertAsync({
@@ -40,8 +41,8 @@ async function customFieldEdit(userId, doc) {
 }
 
 Meteor.startup(async () => {
-  await CustomFields._collection.createIndexAsync({ modifiedAt: -1 });
-  await CustomFields._collection.createIndexAsync({ boardIds: 1 });
+  await ensureIndex(CustomFields, { modifiedAt: -1 });
+  await ensureIndex(CustomFields, { boardIds: 1 });
 });
 
 CustomFields.after.insert(async (userId, doc) => {
diff --git a/server/models/integrations.js b/server/models/integrations.js
index ff199b15c..a2f67dace 100644
--- a/server/models/integrations.js
+++ b/server/models/integrations.js
@@ -5,10 +5,11 @@ import { sendJsonResult } from '/server/apiMiddleware';
 import { ReactiveCache } from '/imports/reactiveCache';
 import Integrations from '/models/integrations';
 import { validateAttachmentUrl } from '/models/lib/attachmentUrlValidation';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.startup(async () => {
-  await Integrations._collection.createIndexAsync({ modifiedAt: -1 });
-  await Integrations._collection.createIndexAsync({ boardId: 1 });
+  await ensureIndex(Integrations, { modifiedAt: -1 });
+  await ensureIndex(Integrations, { boardId: 1 });
 });
 
 WebApp.handlers.get('/api/boards/:boardId/integrations', async function(req, res) {
diff --git a/server/models/lists.js b/server/models/lists.js
index 02a6fbaec..106423664 100644
--- a/server/models/lists.js
+++ b/server/models/lists.js
@@ -8,6 +8,7 @@ import Activities from '/models/activities';
 import Boards from '/models/boards';
 import Cards from '/models/cards';
 import Lists from '/models/lists';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 const hasBoardWriteAccess = (userId, board) => {
   if (!userId || !board) {
@@ -432,10 +433,10 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Lists._collection.rawCollection().createIndex({ modifiedAt: -1 });
-  await Lists._collection.rawCollection().createIndex({ updatedAt: 1, deleted: 1 });
-  await Lists._collection.rawCollection().createIndex({ boardId: 1 });
-  await Lists._collection.rawCollection().createIndex({ archivedAt: -1 });
+  await ensureIndex(Lists, { modifiedAt: -1 });
+  await ensureIndex(Lists, { updatedAt: 1, deleted: 1 });
+  await ensureIndex(Lists, { boardId: 1 });
+  await ensureIndex(Lists, { archivedAt: -1 });
 });
 
 Lists.after.insert(async (userId, doc) => {
diff --git a/server/models/org.js b/server/models/org.js
index e20b0b218..569a49a68 100644
--- a/server/models/org.js
+++ b/server/models/org.js
@@ -1,6 +1,7 @@
 import { Meteor } from 'meteor/meteor';
 import { ReactiveCache } from '/imports/reactiveCache';
 import Org from '/models/org';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.methods({
   async setCreateOrg(
@@ -207,5 +208,5 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Org._collection.createIndexAsync({ orgDisplayName: 1 });
+  await ensureIndex(Org, { orgDisplayName: 1 });
 });
diff --git a/server/models/settings.js b/server/models/settings.js
index 8b40afacc..1f5ff8983 100644
--- a/server/models/settings.js
+++ b/server/models/settings.js
@@ -7,6 +7,7 @@ import { ServiceConfiguration } from 'meteor/service-configuration';
 import Settings from '/models/settings';
 import InvitationCodes from '/models/invitationCodes';
 import EmailLocalization from '/server/lib/emailLocalization';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 const getReactiveCache = () => require('/imports/reactiveCache').ReactiveCache;
 const getTAPi18n = () => require('/imports/i18n').TAPi18n;
@@ -108,7 +109,7 @@ function isApiEnabled() {
 }
 
 Meteor.startup(async () => {
-  await Settings._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Settings, { modifiedAt: -1 });
   const setting = await getReactiveCache().getCurrentSetting();
   if (!setting) {
     const now = new Date();
diff --git a/server/models/swimlanes.js b/server/models/swimlanes.js
index f94e5e3c8..098085c18 100644
--- a/server/models/swimlanes.js
+++ b/server/models/swimlanes.js
@@ -7,6 +7,7 @@ import { ReactiveCache } from '/imports/reactiveCache';
 import Swimlanes from '/models/swimlanes';
 import Activities from '/models/activities';
 import Cards from '/models/cards';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.methods({
   async ensureDefaultSwimlane(boardId) {
@@ -37,8 +38,8 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Swimlanes._collection.createIndexAsync({ modifiedAt: -1 });
-  await Swimlanes._collection.createIndexAsync({ boardId: 1 });
+  await ensureIndex(Swimlanes, { modifiedAt: -1 });
+  await ensureIndex(Swimlanes, { boardId: 1 });
 });
 
 Swimlanes.after.insert(async (userId, doc) => {
diff --git a/server/models/team.js b/server/models/team.js
index 69d0390eb..e337145cc 100644
--- a/server/models/team.js
+++ b/server/models/team.js
@@ -1,6 +1,7 @@
 import { Meteor } from 'meteor/meteor';
 import { ReactiveCache } from '/imports/reactiveCache';
 import Team from '/models/team';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 Meteor.methods({
   async setCreateTeam(
@@ -185,5 +186,5 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Team._collection.createIndexAsync({ teamDisplayName: 1 });
+  await ensureIndex(Team, { teamDisplayName: 1 });
 });
diff --git a/server/models/translation.js b/server/models/translation.js
index baa25def2..a76b61593 100644
--- a/server/models/translation.js
+++ b/server/models/translation.js
@@ -1,5 +1,6 @@
 import { Meteor } from 'meteor/meteor';
 import Translation from '/models/translation';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 const getReactiveCache = () => require('/imports/reactiveCache').ReactiveCache;
 
@@ -50,5 +51,5 @@ Meteor.methods({
 });
 
 Meteor.startup(async () => {
-  await Translation._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Translation, { modifiedAt: -1 });
 });
diff --git a/server/models/userPositionHistory.js b/server/models/userPositionHistory.js
index 51e80499b..7001b31f0 100644
--- a/server/models/userPositionHistory.js
+++ b/server/models/userPositionHistory.js
@@ -3,6 +3,7 @@ import { check } from 'meteor/check';
 import Boards from '/models/boards';
 import UserPositionHistory from '/models/userPositionHistory';
 import { ReactiveCache } from '/imports/reactiveCache';
+import { ensureIndex } from '/server/lib/mongoStartup';
 
 // Reject callers who are not allowed to see the board. Mirrors the guard used
 // by the sibling positionHistory.track* methods (server/methods/positionHistory.js).
@@ -17,11 +18,11 @@ const requireBoardVisible = async (userId, boardId) => {
 };
 
 Meteor.startup(async () => {
-  await UserPositionHistory._collection.createIndexAsync({ userId: 1, boardId: 1, createdAt: -1 });
-  await UserPositionHistory._collection.createIndexAsync({ userId: 1, entityType: 1, entityId: 1 });
-  await UserPositionHistory._collection.createIndexAsync({ userId: 1, isCheckpoint: 1 });
-  await UserPositionHistory._collection.createIndexAsync({ batchId: 1 });
-  await UserPositionHistory._collection.createIndexAsync({ createdAt: 1 });
+  await ensureIndex(UserPositionHistory, { userId: 1, boardId: 1, createdAt: -1 });
+  await ensureIndex(UserPositionHistory, { userId: 1, entityType: 1, entityId: 1 });
+  await ensureIndex(UserPositionHistory, { userId: 1, isCheckpoint: 1 });
+  await ensureIndex(UserPositionHistory, { batchId: 1 });
+  await ensureIndex(UserPositionHistory, { createdAt: 1 });
 });
 
 UserPositionHistory.trackChange = async function(options) {
diff --git a/server/models/users.js b/server/models/users.js
index 2a0207064..aacdceccf 100644
--- a/server/models/users.js
+++ b/server/models/users.js
@@ -11,6 +11,7 @@ import { debounce } from '/imports/lib/collectionHelpers';
 import { Authentication } from '/server/authentication';
 import { sendJsonResult } from '/server/apiMiddleware';
 import EmailLocalization from '/server/lib/emailLocalization';
+import { ensureIndex } from '/server/lib/mongoStartup';
 import ImpersonatedUsers from '/models/impersonatedUsers';
 import Boards from '/models/boards';
 import InvitationCodes from '/models/invitationCodes';
@@ -993,9 +994,9 @@ const startNotificationCleanup = debounce(
 
 Meteor.startup(async () => {
   for (const value of allowedSortValues) {
-    await Lists._collection.createIndexAsync(value);
+    await ensureIndex(Lists, value);
   }
-  await Users._collection.createIndexAsync({ modifiedAt: -1 });
+  await ensureIndex(Users, { modifiedAt: -1 });
   Users.find({ 'profile.avatarUrl': { $regex: '/cfs/files/avatars/' } }).forEach(doc => {
     doc.profile.avatarUrl = doc.profile.avatarUrl.replace(
       '/cfs/files/avatars/',
diff --git a/snap-src/bin/wekan-control b/snap-src/bin/wekan-control
index d1af63f84..ecc75d75f 100755
--- a/snap-src/bin/wekan-control
+++ b/snap-src/bin/wekan-control
@@ -45,11 +45,48 @@ if [ "true" != "${DISABLE_MONGODB}" ]; then
     MONGO_BIN="$SNAP/bin/mongosh"
     MONGO_PORT="${MONGODB_PORT:-27019}"
     MONGO_HOST="${MONGODB_BIND_IP:-127.0.0.1}"
+    # After WEKAN_DB_WAIT_TIMEOUT seconds (default 120) print the English upgrade
+    # guidance once, then keep retrying (large databases can take minutes to
+    # replay the WiredTiger journal after a snap update).
+    WEKAN_DB_WAIT_TIMEOUT=${WEKAN_DB_WAIT_TIMEOUT:-120}
+    db_waited=0
+    db_hint_shown=false
     until "$MONGO_BIN" --host "$MONGO_HOST" --port "$MONGO_PORT" --quiet \
         --eval "try { quit(rs.status().ok === 1 && rs.isMaster().ismaster ? 0 : 1) } catch(e) { quit(1) }" \
         >/dev/null 2>&1; do
+        if [ "$db_hint_shown" != "true" ] && [ "$db_waited" -ge "$WEKAN_DB_WAIT_TIMEOUT" ]; then
+            echo ""
+            echo "========================================================================"
+            echo "WeKan: still cannot connect to MongoDB."
+            echo ""
+            echo "If you just upgraded WeKan or MongoDB, the existing database may have"
+            echo "been created by an OLDER MongoDB version that the new MongoDB cannot"
+            echo "open, so MongoDB never finishes starting and WeKan keeps waiting here."
+            echo ""
+            echo "Upgrade the database - dump with the old version, restore with the new:"
+            echo "  1. Start the OLD, previously-working MongoDB version."
+            echo "  2. Back up:   mongodump --archive=wekan.archive --gzip"
+            echo "  3. Stop old MongoDB. Start the NEW MongoDB on an EMPTY data dir."
+            echo "  4. Restore:   mongorestore --archive=wekan.archive --gzip --drop"
+            echo "  5. Start WeKan again."
+            echo ""
+            echo "Attachments and avatars are stored ON DISK under WRITABLE_PATH, NOT"
+            echo "in MongoDB, so when moving to a new server ALSO copy that whole"
+            echo "directory (it contains 'files', 'attachments' and 'avatars'):"
+            echo "  - Snap:   /var/snap/wekan/common/files"
+            echo "  - Docker: the 'wekan-files' volume mounted at /data"
+            echo "  - Source: the WRITABLE_PATH you configured"
+            echo ""
+            echo "Also check the MongoDB log (snap logs ${SNAP_NAME:-wekan}.mongodb) for"
+            echo "the real reason: incompatible featureCompatibilityVersion, wrong mongod"
+            echo "version, or an unclean shutdown needing 'mongod --repair'."
+            echo "========================================================================"
+            echo ""
+            db_hint_shown=true
+        fi
         echo "MongoDB not ready yet, retrying in 5 seconds..."
         sleep 5
+        db_waited=$((db_waited + 5))
     done
     echo "MongoDB replica set primary is ready."
 fi
diff --git a/start-wekan.bat b/start-wekan.bat
index 54d3d58a8..34222d922 100644
--- a/start-wekan.bat
+++ b/start-wekan.bat
@@ -749,6 +749,58 @@ REM #node --stack-size=65500 main.js
 
 REM #-------------------- OPTIONAL SETTINGS END --------------------
 
+REM #-------------------- WAIT FOR MONGODB TO BE READY --------------------
+REM # Do not start WeKan until MongoDB is reachable and a primary is elected,
+REM # otherwise the first index creation crashes with "Topology is closed".
+REM # After WEKAN_DB_WAIT_TIMEOUT seconds (default 120) the English upgrade
+REM # guidance is printed once; WeKan keeps retrying after that.
+IF "%WEKAN_DB_WAIT_TIMEOUT%"=="" SET WEKAN_DB_WAIT_TIMEOUT=120
+SET DB_WAITED=0
+SET DB_HINT_SHOWN=false
+ECHO Waiting for MongoDB to be ready at 127.0.0.1:27017...
+:wait_for_mongodb
+mongosh --port 27017 --quiet --eval "try { quit(db.hello().isWritablePrimary ? 0 : 1) } catch (e) { quit(1) }" >NUL 2>NUL
+IF %ERRORLEVEL% EQU 0 (
+   ECHO MongoDB is ready.
+   GOTO mongodb_ready
+)
+IF "%DB_HINT_SHOWN%"=="false" IF %DB_WAITED% GEQ %WEKAN_DB_WAIT_TIMEOUT% (
+   ECHO.
+   ECHO ========================================================================
+   ECHO WeKan: still cannot connect to MongoDB.
+   ECHO.
+   ECHO If you just upgraded WeKan or MongoDB, the existing database may have
+   ECHO been created by an OLDER MongoDB version that the new MongoDB cannot
+   ECHO open, so MongoDB never finishes starting and WeKan keeps waiting here.
+   ECHO.
+   ECHO Upgrade the database - dump with the old version, restore with the new:
+   ECHO   1. Start the OLD, previously-working MongoDB version.
+   ECHO   2. Back up:   mongodump --archive=wekan.archive --gzip
+   ECHO   3. Stop old MongoDB. Start the NEW MongoDB on an EMPTY data dir.
+   ECHO   4. Restore:   mongorestore --archive=wekan.archive --gzip --drop
+   ECHO   5. Start WeKan again.
+   ECHO.
+   ECHO Attachments and avatars are stored ON DISK under WRITABLE_PATH, NOT
+   ECHO in MongoDB, so when moving to a new server ALSO copy that whole
+   ECHO directory - it contains 'files', 'attachments' and 'avatars':
+   ECHO   - Snap:   /var/snap/wekan/common/files
+   ECHO   - Docker: the 'wekan-files' volume mounted at /data
+   ECHO   - Source: the WRITABLE_PATH configured in start-wekan.bat
+   ECHO.
+   ECHO Also check the MongoDB log for the real reason: incompatible
+   ECHO featureCompatibilityVersion, wrong mongod version, or an unclean
+   ECHO shutdown needing 'mongod --repair'. WeKan keeps retrying every 5s.
+   ECHO ========================================================================
+   ECHO.
+   SET DB_HINT_SHOWN=true
+)
+ECHO MongoDB not ready yet, retrying in 5 seconds...
+timeout /t 5 /nobreak >NUL
+SET /A DB_WAITED=%DB_WAITED%+5
+GOTO wait_for_mongodb
+:mongodb_ready
+REM #----------------------------------------------------------------------
+
 ECHO Starting Wekan in a persistent cmd loop...
 
 :start_wekan
diff --git a/start-wekan.sh b/start-wekan.sh
index f27fdec9c..95fa0a703 100755
--- a/start-wekan.sh
+++ b/start-wekan.sh
@@ -30,6 +30,54 @@
           USE_CHANGE_STREAMS=false
       fi
       #----------------------------------------------------------------------
+      #-------------------- WAIT FOR MONGODB TO BE READY --------------------
+      # Do not start WeKan until MongoDB is reachable and a primary is elected,
+      # otherwise the first index creation crashes with "Topology is closed".
+      # After WEKAN_DB_WAIT_TIMEOUT seconds (default 120) the upgrade guidance
+      # below is printed once (English only); WeKan keeps retrying after that.
+      if command -v mongosh > /dev/null 2>&1; then
+          WEKAN_DB_WAIT_TIMEOUT=${WEKAN_DB_WAIT_TIMEOUT:-120}
+          db_waited=0
+          db_hint_shown=false
+          echo "Waiting for MongoDB to be ready at 127.0.0.1:27017..."
+          until mongosh --port 27017 --quiet --eval 'try { quit(db.hello().isWritablePrimary ? 0 : 1) } catch (e) { quit(1) }' > /dev/null 2>&1; do
+              if [ "$db_hint_shown" != "true" ] && [ "$db_waited" -ge "$WEKAN_DB_WAIT_TIMEOUT" ]; then
+                  echo ""
+                  echo "========================================================================"
+                  echo "WeKan: still cannot connect to MongoDB."
+                  echo ""
+                  echo "If you just upgraded WeKan or MongoDB, the existing database may have"
+                  echo "been created by an OLDER MongoDB version that the new MongoDB cannot"
+                  echo "open, so MongoDB never finishes starting and WeKan keeps waiting here."
+                  echo ""
+                  echo "Upgrade the database (dump with the old version, restore with the new):"
+                  echo "  1. Start the OLD, previously-working MongoDB version."
+                  echo "  2. Back up:   mongodump --archive=wekan.archive --gzip"
+                  echo "  3. Stop old MongoDB. Start the NEW MongoDB on an EMPTY data dir."
+                  echo "  4. Restore:   mongorestore --archive=wekan.archive --gzip --drop"
+                  echo "  5. Start WeKan again."
+                  echo ""
+                  echo "Attachments and avatars are stored ON DISK under WRITABLE_PATH, NOT"
+                  echo "in MongoDB, so when moving to a new server ALSO copy that whole"
+                  echo "directory (it contains 'files', 'attachments' and 'avatars'):"
+                  echo "  - Snap:   /var/snap/wekan/common/files"
+                  echo "  - Docker: the 'wekan-files' volume mounted at /data"
+                  echo "  - Source: the WRITABLE_PATH configured in start-wekan.sh"
+                  echo ""
+                  echo "Also check the MongoDB log for the real reason (incompatible"
+                  echo "featureCompatibilityVersion, wrong mongod version, or an unclean"
+                  echo "shutdown needing 'mongod --repair'). WeKan keeps retrying every 5s."
+                  echo "========================================================================"
+                  echo ""
+                  db_hint_shown=true
+              fi
+              echo "MongoDB not ready yet, retrying in 5 seconds..."
+              sleep 5
+              db_waited=$((db_waited + 5))
+          done
+          echo "MongoDB is ready."
+      fi
+      #----------------------------------------------------------------------
       cd .build/bundle
       #-------------------- USING MONGODB CHANGE STREAMS WITH REPLICA SETS AT CURRENT DATABASE --------------------
       # If you would not like to use Change Streams and replica set for improving speed, change to use polling: