I've exactly your issue. I've released an app update recently with new Entities and some users (not all the users) are encountering an issue with app sync. They have also tried to uninstall and install the app again without results. The really strange thing is that on each device, when data is downloaded from iCloud, two different versions of the library are restored, exactly the one that was previously on that particular device.

I'm having the same error only on the Mac Catalyst build with no significant changes to my source code: ITMS-90338: Non-public API usage - The app contains or inherits from non-public classes in Contents/PlugIns/BookTrackWidgetsExtension.appex/Contents/MacOS/BookTrackWidgetsExtension: UIPrintPageRenderer, UISimpleTextPrintFormatter ,The app contains or inherits from non-public classes in Contents/PlugIns/BookTrackIntentHandler.appex/Contents/MacOS/BookTrackIntentHandler: UIPrintPageRenderer, UISimpleTextPrintFormatter ,The app contains or inherits from non-public classes in Contents/MacOS/Book Track: UIPrintPageRenderer, UISimpleTextPrintFormatter . If method names in your source code match the private Apple APIs listed above, altering your method names will help prevent this app from being flagged in future submissions. In addition, note that one or more of the above APIs may be located in a static library that was included with your app. If so, they must be removed. For further information, visit the Technical Support Information at http://developer.apple.com/support/technical/ What could I do?

Was the problem fixed in iOS 14 beta 4? If the answer is no, which could be the strategy to approach this problem?

I've seen that the documentation of NSPersistentCloudKitContainer has been updated after the WWDC with two new Type Properties: class let eventChangedNotification: NSNotification.Name and class let eventNotificationUserInfoKey: String I think that are related to your question but I haven't tried them. I'm looking for this feature from the last year and I hope that in iOS 14 it will be implemented.

Have you found any solution to this problem? I've the same issue with a one-to-many relationship which is managed correctly in Core Data but is not synced on iCloud and at the next restart the relationship is restored.