Face ID Failing After Installing iOS 16.3.1

About 36 hrs after upgrading my iPhone 11 to iOS 16.3.1 Face ID stopped working. Until then Face ID had always worked flawlessly. It refused to unlock the phone and forced me to enter the passcode to unlock it. I tried cleaning the notch, retrying unlock, nothing helped. After several failed unlock attempts I got a message saying "Face ID unavailable, try again later".

Eventually I tried resetting Face ID and tried to set it up again, but during the face scan process I got the Face ID not available, try again later message. I then tried restarting the phone and went back into Face ID setup and it failed again, but on the second or third attempt it suddenly worked and I could complete the Face ID setup process. From then on Face ID was working again. For about 24 hrs. Then it just stopped working again (this time I didn't get the unavailable, try again later message, it just wouldn't unlock).

This time I powered the iPhone off and on again and it still failed to unlock without the passcode a few times, but then suddenly started working again for no obvious reason.

I guess it could be an intermittent h/w issue, but I'm suspicious that iOS 16.3.1 may be causing the problem, has anyone else encountered issues with Face ID after updating to 16.3.1?

I'm also curious about the meaning of the message "Face ID unavailable, try again later" and what sort of issue(s) would trigger that? What sort of problem would cause Face ID to fail temporarily and waiting a while might resolve? Temperature or something?