I'm replying to this topic because its very similar to my issue.
I tried resetting 'Face ID' (by going into the app settings, turning off the 'Face ID' toggle for the app, then turning it back on, however the issue persists).
The issue is Face-ID ONLY shows the first time the app is open. If I open Enpass, copy a password to the clipboard, swipe over to Chrome/Safari/etc, then swipe back to Enpass... it'll ask for my Master Password every time. It will not attempt to use Face-ID, and it does not have a Face-ID icon.
If I force-quit Enpass, it'll correctly use Face-ID upon next launch.
I tried this on my iPad Pro 11 and it appears Face-ID shows every time (along with the Face-ID icon). So the issue appears to only present on my iPhone X as of now. Screenshot after swiping back to Enpass is attached (showing no Face-ID icon).
What should happen?
When I open Enpass 6.0.1 on my IPhone X and send it to background via the Home-Button (swipe) and open it again the Face-ID verification should appear.
What happened instead?
Face-ID verification does not appear. It asks for Master-Password
IOS 12.1.2 (16C101)