EDIT: 5 August, 2021 (10:40 UTC): The fix is now live and this issue has been resolved
5 August, 2021 (09:00 UTC): There is a known issue that is affecting loading game progress from Game Center on iOS. Switching between Game Center accounts is not working at the moment. Please do not uninstall your game before this problem is fixed.
In the meantime, we will continue to update this announcement with further information. We apologise for any inconvenience caused by this!