I have the same problem on my Samsung S8+. But what you suggested does not help: "In Enpass v6 choose to restore data from Backup File → Local Storage and locate the downloaded backup." - How can I restore a backup when I am not able to log in?
And it work perfectly on my Win10 laptop.
In th old enpass v5 on my phone I had activated fingerprint authentication, but that option is no longer available.
Regards,
Arve