Odd Behavior from Face ID re Beard

Two days ago Face ID stopped working 95% of the time to open apps, but still worked 100% of the time to unlock the phone. The error message was that it did not recognize my face. This behavior repeated on every financial app I have plus my password manager. I reset my Face ID, rebooted the phone, checked for camera obstructions, checked for updates, and everything else on the official troubleshooting page, plu sa few other ideas I came up with, and it made no difference.

Then yesterday afternoon I trimmed my beard which I do every 2-3 weeks. And suddenly since then Face ID has worked perfectly in every application, without any other intervening event. Seeing as I had just I reset my face on the phone the day before, the fact that my beard was a little scragglier than usual should not have made a difference, and if the beard was the problem, resetting my face from scratch as I did should have fixed it. Also, FWIW, I started the beard about 10 months ago and that had no discernible effect on how Face ID worked.

One other note, I noticed previously that Face ID is sometimes less forgiving when opening apps than the phone itself. Which I guess makes sense, especially for financial apps. Maybe Apple allows app makers to require a higher degree of match than the phone baseline (which is pretty high). So I suppose that is what was happening here. But no matter what it should still be able to handle a beard especially if you reset your face with the beard in place. It’s wasn’t even that big or shaggy compared to lots of other guys.

Sine it works now, I do not need a solution. But I'm wondering if this behavior has been seen before or if someone can offer an explanation. Thanks, I find it very curious.