In 1.38 I noticed that weird issue.
I have to quit and restart the game.
If I zoom in enough they appear, zoom out and just white squares.
I’ve had this in 1.38 too, I don’t think it was from the screensaver though, it happened when I was hooking the game up with Open Broadcaster for recording. Went back to the game and the graphics had gone.
Just happened in 1.39, while adding somthing to this forum
I’ve noticed the same. Only had it one when I Alt-Tab over from Google Chrome. Done it loads of times and never had an issue. Just the once so didn’t think to mention it.