I’m also facing this issue. I used FaceID to get into my phone to do the iOS14 update and when it had finished FaceID no longer worked. I originally thought it might be a bug cause I had updated to the iOS14 Beta so I thought maybe Apple was still working through the kinks in their system. However, even on the official iOS14 it’s still broken. I went into Apple the other day and they told me that the FaceID sensor HARDWARE was broken and that since I was out of warranty (I have an XS Max) they couldn’t make any exceptions and I would have to buy a new phone..... really??? All I did was update your software! I’m going to try and reach out to them again so wish my luck!
To summarize though, the issue I’m having is my front camera works, but when setting up FaceID it can’t register my face all the way so it says “Move iPhone a little higher/lower” forever. I’ve tried restarting, resetting FaceID data, factory resetting my phone, nothing works. If you’re having this issue then Apple may have broken your actual hardware and now won’t fix it.