I have also just encountered this issue.
Windows 10 Pro x64 1803, Edge Browser, Enable browser extensions was already enabled.
Enpass Extension for Edge Browser v5.5.2
Enpass Desktop (Windows Store bridged) v5.6.6
I generally see these issues when the Windows Desktop app is locked, and I then click on the Enpass browser extension button to invoke Enpass. It is as though it is not always cleanly handling communication to the locked desktop app.