Please check if your game is synced to the correct Google Play Game or iCloud account:
If you've recently changed devices or deleted and reinstalled the game, make sure that your game is synced to the correct account. This will ensure that your progress is saved to the cloud.
Offline play is available but as the game stores data using Google Play Games and iCloud it needs internet connection to keep your data safe. Although you can play offline, there is the chance of this type of thing happening when you reconnect.
Check if the game data is corrupted: If you're experiencing technical issues or crashes, it's possible that your game data has become corrupted. Try uninstalling and reinstalling the game to see if this resolves the issue.