Please try the following:
- Open your Settings app and confirm that:
- You are signed in to iCloud
- You are signed into Game Center
- The Apple IDs used for both sign-ins are the same
- Restart your device
- Make sure that you fully turn it off (don't just put it to sleep) and then turn it on again. Both shutting down and starting up take at least a few seconds, so if either of those seemed to be instantaneous then you probably just put the device to sleep--please try again!
- Check your device's internet connection by opening Safari and going to a webpage of your choice. Confirm that there are no problems connecting to that webpage.
- Skip this step if playing on Apple TV—there is no Safari on Apple TV.
- Launch the game. Hopefully the problem has been resolved!