Try the following:
- Restart your device.
- Reinstall the game and reconnect it to Google Play Games (the green joystick icon on the main game screen) if it was previously connected.
If that doesn't fix the problem, contact our customer support and provide the following information:
1. A detailed description of the problem.
2. What happened before your progress was lost (you reinstalled the game, changed devices, updated the software, etc.).