I ran into the same problem. Setting up a shared app group between the app and the XPC Service, as Eskimo suggested, solves the problem and works really well. Thanks!

Thanks for explaining that Transaction.updates does not work with iOS 15.2—I spent the past week troubleshooting this issue under iOS 15.2, and switching to iOS 15.0 solves the problem. I'm using Xcode 13.2.1.

I have this issue as well on macOS 12.5. Good to know that padding can play a role. I have not been able to find a practical work-around; for example, using Rectangle instead of padding brings the artifact back. Reportedly, the artifact is gone in macOS 13 beta https://stackoverflow.com/a/73615876/668253.