If you're signed into Google Play or Gamecenter:

Please sign out of your Google Play/Gamecenter account on your device and relog into it, then relaunch the game.

If this doesn't work, please try clearing your Google Play or Gamecenter app caches:

Phone Settings > Apps > Google Play Services > Storage & Cache > Clear Cache

And/Or

Phone Settings > Apps > Google Play Games > Storage & Cache > Clear Cache as well if the above doesn't work