After further experimentation I have discovered it only occurs on one phone. I attribute this to the Call Extension API still being very buggy and unstable even in released software.
Many times during the past few months I have noticed more than one phone gets completely stuffed up - calls never ever ever get connected, blocked numbers aren't blocked, identified number remain identified forever even after being unregistered via the Call extension and even after the app is deleted etc.
I am 100% utterly utterly convinced the Call Extension API can misbehave and permanently put the device into an unstable state which a restart does not fix and a factory data reset is necessary.
I’m sorry you’re having such a poor experience with this stuff. I haven’t posted on this thread because I don’t have any direct experience with it. However, my usual advice applies: if you can find a way to reproduce these problems, please do file a bug, and then post your bug number, just for the record.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"