Facial recognition not working for lock screen. OK for apps though

Facial recognition has been working fine for months and I haven't done a recent update. Suddenly it has stopped working, but just for the lock screen. It is absolutely fine for my apps. I can't seem to reset it either because every time I get the message 'facial recognition not available. Try later'

I am not wearing a mask or sunglasses or anything that is likely to interfere with it and I have cleaned my camera lens

What is happening??