Face ID has been disabled

See and follow the Related Article linked above. If that procedure fails, contact Apple Support and schedule what will probably be a repair. To disucss this with Apple Support, use the Get Support link in the upper right of this webpage.

See if anything here helps 

If Face ID isn't working on your iPhone or iPad Pro  *

Face ID not working.   -

Face ID not working' problems on iPhone.    -

Fix iPhone X Face ID Not Working.    -

Face ID Not Working.   -