If I leave everything as default and use the setup screen to copy the files from the directory I was previously trying to use, it works fine. It definitely seems to be a problem with selecting a different directory as the game files directory.
I don't know how that part works, never used it actually.
I'll try to have a look at it eventually, but right now I'm not in a mood to install Android Studio.
If someone wants to help, it would be most welcome...