Cryptomator window/GUI not showing on Windows 10

I am running Cryptomator version 1.6.11-x64 on Windows 10.

When I start cryptomator I get the icon on the taskbar.
Right-clicking on the icon shows “Show”, “Preferences”, the three latest vaults I have opened and “Quit”. I can unlock any of the three vaults from there but even if I try and click “show” I cannot see the GUI, all I get is another icon on the taskbar showing it should be open.
Using Alt Tab I can see that it should be visible, but it looks very odd with a transparent (!) window, with the icon and a green line on top…

The logfile seems to be ok - but I’m not a specialist.

So, looking for help or good suggestions