An app that I'm working on uses CloudKit with various CKSubscriptions which started to work well again after the 503 errors began disappearing. However, after upgrading my iPhone 7 to iOS 15.3 my app does not receive background push notifications anymore. All the CloudKit subscriptions that use CKSubscription.NotificationInfo(shouldSendContentAvailable: true) do not work anymore, i.e. the AppDelegate's application(_: didReceiveRemoteNotification: fetchCompletionHandler:) method is no longer called.
Actually, after rebooting the device my app receives one single notification, the first one that arrives, but not more.
The app runs still fine on macOS 12.1 and tvOS 15.2 and it was running fine on iOS 15.2.1 before the upgrade.
Anyone seeing similar issues or have ideas that could help? I filed a report on the feedbackassistant but I don't expect much help from there.
Installing the current iOS 15.4 beta solved the issue for me (see also this thread).