It is a hot topic about
iPhone X Face ID not available after screen replacement in repair industry. Generally, replacing screen will not affect the normal use of Face ID. With REWA has done some further researches and guess the problem is caused by improper operations during the repair, which results in the damage of flex cables or other components. Their do a very nice video to show how their repair iPhone X face ID failure after changing screen.
Video link:
https://blog.rewatechnology.com/fix-...d-not-working/