https://bugs.winehq.org/show_bug.cgi?id=41403
--- Comment #12 from Tobias (:Tobbi) Markus tobbi.bugs@googlemail.com --- I just investigated more:
It works again now, though nothing changed about my wine prefix.
However: When I switch the App to Fullscreen and back to windowed mode again, the same thing is happening, which (uneducated guess) could have something to do with OpenGL contexts that get invalidated incorrectly or so.
If you want some logs, I can certainly provide them.