My iPhone Xs Face recognition failed 3 weeks ago. No reason, it just stopped working.
Did a backup to iCloud
Then check if there was any updates to ios
The did a factory re install
Re check the FaceiD and got same error message. Something about the phone had overheated
Called Apple support
They said get appointment at Apple Genius bar. They were very helpful and quick
The later same day the Apple centre genius bar called and said don't bother to come in because I'd done all the thing they themselves would do and recommended I call my iPhone seller (John Lewis) as the phone wa only 18th old.
Up to this point was less and 60 mins
3 hour later after calling JLewis/chat /call centre nightmare they agreed I'd purchased it from them and I could send it back for repair/exchange
It took 3 week and lots of call but eventually got a new replacement.
Seems the FaceID IR illuminators sometime fail and cannot be repaired
Anyway... that's my story I hope it helps
Takeaway? If you buy your devices get iPhone insurance or Buy from John Lewis so you get 2 year warranty or I guess rent your phone which might include cover. Apple store would have done a swap for £580, which given the phone was £1198 new and only 18 months old was great news. Shame my iPhone 5s lasted 9 years