Big random symbols glitching on a black screen

[Amek747PL]

I was playtesting a map made on a my server (using "Superfighters Deluxe Server.exe", not the in-game hosting option). Some time after I started playing (same time when I set up the server) - half an hour maybe? - my screen started glitching out, showing only big, white SFD font symbols. They were constantly changing. In the background, you could also see the shape of some of the solid tiles in the map.
I could fix it by Alt+Tab'ing, but then it would show up again after a while.
When I pressed escape, the symbols dissaperad, but some of the tiles were still glitched and the screen remained black. I couldn't make screenshots showing it, because they showed nothing (purple screen with random glitched spots), so I took some photos with my phone. They are available here. I had Spotify playing music in the background. Microsoft Word, Chrome and Discord were also running. I closed the game but then I tried to recreate it and record it with my phone but despite recording for 17 minutes nothing like that showed up again. Someone on Discord suggested it could be something with fullscreen.

[Gurt]

Sounds and looks like a graphics driver related problem, something we can't fix.
Here's some general advice: Update your graphics driver. Restart your computer.