iPadOS17.8 beta not syncing our app

We use a test iPad to test new versions of our app as well as checking new (beta) versions of iPadOS. Our app - Rendezvous Appointment Book -uses iCloud to sync between the iPad and iPhone. So, when an entry is made on either the iPad or iPhone the entry is automatically synced to the other device(s). So, a user can make a client appointment on one device and it syncs to another iPad or iPhone logged into the same iCloud account. This has worked smoothly for years. But, the latest beta version - 17.8 caused a syncing issue where all the existing data that is stored on the same iCloud account did not sync.

We have seen this before.

Recently, starting with iPadOS/iOS 16.3 syncing failed for a number of users just on their iPads. The data stored on iCloud disappeared, but the iPhone did sync with iCloud. About 30 users could not get their data to sync at all , but the vast majority did sync. Some users who experienced the problem were able to sync by deleting the app and reinstalling it from the App Store, as per our recovery instructions. Then when version 16.4 was released all syncing worked as well as 16.5 and 16.6 which have worked perfectly.

When 17 beta was released we tested again for proper syncing, but ran into the same issue with version 17.3 beta - no sync again. But 17.6 beta did sync. Now, in testing this last Thursday with 17.8 beta the same issue reappeared on our test iPad.

We contacted Apple Developer support but have yet to get any resolution (and we are worried that when Apple releases 17 on Sep 11 the syncing issue might still rear its ugly head).

Has anyone seen this happen? BTW all other iCloud syncing worked correctly, e.g. Photos, backups, etc.