Apple support is almost always the best resource when a release feature is stuck since they have all the cards (server side data, notes from the engineers, and latest reports of issues whether it’s a trickle or a flood of user feedback).
That being said, if I had to troubleshoot this without contacting Apple, the first thing is I would turn off FaceID on my device and then power it off.
Next thing would be to review my Apple ID from an iPad or computer on the web so that it meets the three other requirements: significant locations enabled, Find My enabled and two factor security on your AppleID.
I would ensure two factor was set before turning on the phone and checking. Next when the phone is on, clean up at least one “significant location” to be sure that’s working. Next, review Find My for that phone. Now, enable Face ID and re-check.
Keep notes, as contacting Apple support is really the best way for this until others can reproduce the issue (and perhaps Apple needs to retest it on older hardware or perhaps even issue a fix in an update).
