I can't see this having been reported here before, but it seems the game as of recently doesn't like being fullscreened on linux with a 4k monitor.
I think the last time it worked fine was 6.2 or 6.3 (I don't remember which one was the last I could fullscreen on) but has been broken since at least 6.6. (I don't have any older versions on hand to test)
The game goes like this if you maximize or fullscreen, and images will not load anymore.
Quitting the game and playing it without maximizing or fullscreening works perfectly fine though, just a less than ideal experience with a small window on a 4k display.