Samsung
Turn Auto Sync On or Off for Accounts auf Samsung
Automatic data sync keeps every account on your Samsung phone up to date in the background. When it is active, apps like Contacts, Calendar or Photos pull new data as soon as changes happen on the server, without you opening the app first.
If entries stop appearing or updates lag behind what you see on other devices, the sync setting for that account has usually been turned off, either by you or automatically to save battery. This is controlled centrally, not per app.
To check or change it, go to Settings ➔ Accounts and backup ➔ Manage accounts. From there you can enable or disable Auto sync data for all accounts at once, or tap into a single account to sync only that one.
Turning sync off is useful when you want to limit background data usage or extend battery life, especially while traveling. The trade-off is that new emails, contacts or backups will not appear until you open the app and refresh manually.
If only one app misbehaves while others sync fine, the issue is more likely an app-specific permission or a signed-out account rather than the global auto sync setting.