Ok, so I understand that you have to use PIN or password after reboot, after 24 hours and all that. I do not have smart lock enabled, and I'm not using any screen app locks to my knowledge... yet, when my phone sits for just 15 minutes sometimes it will ask me to use fingerprint or PIN instead of face unlock as required by the security policy. It actually seems like the face unlock is mostly useless, as it asks this quite often. I can't even seem to find a rhyme or reason as to when or why it will use face unlock 5 times in a row sometimes and then other times make me do the PIN or fingerprint after just using face unlock once. ANY ideas? I don't think I noticed this before maybe a week or two ago after last update.
Go to Settings > Apps and Click on the 3 Dot Menu MIDDLE Right & Toggle ON "Show System Apps" > Search for "Biometrics" and Clear Both Cache & Data for Biometrics & Reboot.
You will have to Register your Finger Prints & Face again.
See if that fixes the issue, because, no it's not normal.