Have you reinstalled the game? Changed your device? Are you playing on two devices? It may happen that you need to restore or sync your game progress.
iOS
As you play, the game progress is automatically stored in the iCloud (assuming the iCloud account is properly configured). When you reinstall the game and login to the iCloud again, you will be presented with a dialog asking if you’d like to restore your game progress or continue playing with the new one. Please be careful with your selection as this choice is irreversible!
Android
The game progress is stored after you log in to Google Play Games. When you reinstall the game and login to the Google Play Games again, you will be presented with a dialog asking if you’d like to restore your game progress or continue playing with the new one. Please be careful with your selection as this choice is irreversible!