Thanks for the finds, Morac and sharp65. That's some good stuff. Much further progress than we've had so far.
That Apple thread concerns me. I spoke with a Senior Advisor today who's getting in contact with the engineering team, and they're supposed to contact me again next week. I hope they don't come back and tell me to factory reset my phone as new. That would be a pain, especially since that Apple thread proves that a factory reset as new doesn't work.
At this point doing a factory reset seems pointless, since once you sign in with your Apple ID the problem will return.
One thing I would be curious about is if logging in with a different Apple ID would allow updating. Something like the Apple TV that supports multiple accounts might be a good place to test that.
I spoke to another senior advisor today and apparently there was a mixup on when I thought I was supposed to get a callback. It is scheduled for tomorrow morning, so hopefully by then I’ll have more details. That makes sense as the SA contacting engineering last night and I wouldn’t expect a turnaround time the next morning. I’m told most Apple ID issues take at least 48 hours to fix.