White circle on lock screen / Face ID not working

Recently on my iPhone 11, there’s been this white circle in motion on the top of the lock screen that I’ve never seen before. When I swipe up to unlock, it’ll say Face ID as usual, but nothing happens and a

couple seconds later it’ll ask me to enter passcode instead. I have all the Face ID options turned on in the Settings. So for the past couple days, I’ve only been able to unlock the phone with passcode. Anyone know what the circle means and / or how to fix this?