Same problem here.
Under iOS 12.1.2, Enpass 6.0.0 (196) works fine. I was also able to synchronize with WebDav on my Synology NAS without any problems. All works well. But when I turn off the NAS, Enpass freezes on iPhone and can't operate menus anymore. Password fill in works but still .
If I switch NAS on again, everything works again.
Enpass searches run the connection to the NAS and if he doesn't find it, Enpass freezes.
From my point of view, it should only be triggered as needed and by hand.
P.S. The desktop under Windows simply gets an error message. Synchronization error.