Hey!
I suspect it’s some very serious VirtualBox bug, so for now it’s unusable for me as well, take a look here
P.S. Btw although initially i’ve said only Windoze - it’s also happens for Linux guests,for example if i start to update existing VM it will first blink with some colors (which kinda tells that it might be video related), but then it’s doing all kinds of integrity check failures etc, terminal crashes, then vm might crash…It’s a disaster.
What’s your GPU btw, Nvidia?