The first post in this thread may have the same problem as I have.
I don't have a solution, only a theory as to why, that I described here:
So, uninstall the Windows Store App and install the Traditional Win32 application instead, while Enpass sort out their App. @JürgenO above seems to also have a non-english character user account name, right? @Unstiglitz, here is a wild guess at helping you: it requires some computer experience. Try it at your own risk...
First, do not uninstall the Windows Store App.
If the App auto-updated the vault may still be there, just that the buggy new version can't find it. Go to
C:\Users\XXXXXX\AppData\Local\Packages\SinewSoftwareSystems.EnpassPasswordManager_fwdy0m65qb6h2
where XXXXXX is your user account name, and also the last bit may differ, it seems kind of random.
If you find that folder, there should be a subfolder LocalState, and in that one, a folder Vaults, then lastly "primary".
There, you should hopefully find at least two files:
vault.enpassdb
vault.json
and I also had a "fc19cda3-6d60-4443-b283-d036928dfc44.enpassattach"
Copy these to another folder temporarily.
Now, install the Traditional Win32 application.
Start it and say you are a new user, and set up a new vault. Never mind the password or any contents...
Close the application and also quit the system tray Enpass icon: right click, menu to the left, quit.
Go to C:\Users\XXXXXX\Documents\Enpass\Vaults\primary
where again XXXXXX is your user account name. This is where the Win32 application stores its data.
At this point there is likely only two vault files there.
Now copy your "rescued" files from above, to this location, replacing the files already there.
Now, restart Enpass from the start menu. Your old vault should be there, accessible with your old password.
And lastly: do set up a cloud synchronization!
Good luck!
/Håkan, Sweden