On this page
Read the warning
Open Nextcloud's administration overview and record the exact warning and time. Check whether the problem affects browser access, all clients, or one device. Preserve unsynced local files before reconnecting a client.
Background jobs
Nextcloud recommends system cron for production background jobs. Confirm the job uses the correct OS account, PHP version, and installation path. Container deployments have their own scheduling method; do not copy host commands into an unrelated layout.
Check storage and access
Verify free disk space, HTTPS, proxy configuration, and the affected user's quota. Never solve a sync warning by deleting the server data directory or forcing a database reset.
Recovery requires several parts
Protect the data directory, configuration, database, and any custom theme or application material needed by your installation. Test restoration separately before an update.