Thank you for Windows Hello support but it is not working very well.
If I put the app in the background and then start it back up using the start screen tile or the All apps list Windows Hello pops up for a second and then disappears asking for the master password. If I hold down the back button to bring the app back up it works.
I can get it to work again by exiting the app completely.
Good luck fixing this!
Enpass v5.1.1
Windows 10 mobile v10.0.14372.0