I may have seen something similar, but it's not consistent nor common. I've seen artifacting on KDE lockscreen and I think I've had 2 lockups since upgrading to plasma 6.

I'm in an AMD GPU (6650XT) with an older CPU (5600X) on an old motherboard (X370 from OG Ryzen launch).

If your have more details, I'll see if I can repro. My system is pretty stable though, and I use my computer almost every day (kids use it to pay games, I do SW dev). It mostly just runs Firefox and Konsole, and sometimes Steam and a handful of other apps (Godot, Multi MC for Minecraft, some authenticator app I got from Flathub).