This problem may be occurring because your iCloud storage is close to the limit and automatic saves and backups during play are failing.
We apologize for the inconvenience, but please try playing the game in an environment that does not use iCloud, such as playing on your device offline, and check whether the problem occurs.
If the problem is resolved in an offline environment, please consider increasing the available space in your iCloud storage, referring to the following page.
Manage iCloud Storage (This will take you to the Apple website)
https://support.apple.com/en-us/108922