CloudKit subscriptions are created successfully but notifications don't arrive

Question

I have a macOS app currently in development and an iOS app that has already been released.

The iOS app was built using the SwiftUI life-cycle and the macOS app is being built with AppKit. (I'm not sure if it may be relevant or not).

I'm trying to enable the macOS app to receive notifications about record changes so it can refresh its UI automatically with the latest records.

The iOS app is being tested via TestFlight on a real device and both apps are using the proper CloudKit environment. The subscriptions also appear on the CloudKit console, so they are being created successfully by the macOS app.

However, when I try to create records on the iPhone, the macOS app doesn't get notified at all. The record changes appear in CloudKit console logs and they are being stored in the database, but the subscription notifications, for some reason, are not being fired (at least I don't see any log entry that could be possibly related to push notifications).

There are times when a CloudKit notification arrives at the macOS app as it's printed on the Xcode console, but I don't know exactly why, since it doesn't appear right after manual database updates.

I can post some snippets if necessary.