I have a weird bug which occurs usually after I get my laptop out of sleep mode:
The lock screen is checkered green and red rectangles (my background is visible as the rectangles are somewhat transparent), and after I unlock I get similar squares in some applications, namely the desktop icon labels. I also get a KWin notification:
KWin Window manager,
Desktop effects were restarted due to a graphics reset
Which then reappears periodically. The time displayded on the taskbar's digital clock also jumps back to correct time after this notification.

The bug only happens after I use sleep mode, there is no visible problem from start up until I use sleep mode. It started after I used up all my GPU's memory training neural networks.

System Information:
  • Kubuntu 19.04 (on a dual boot with WIndows 10)
  • Dell Precision 7720 Laptop
  • CPU: 2*8 GiB AMD SODIMM DDR4
  • GPU: NVIDIA Quadro M1200 Mobile
  • GPU driver: NVIDIA driver metapackage from nvidia-driver-418 (the recommended one in a list of 3 in driver manager)
  • plasmashell 5.15.4
  • Qt: 5.12.2
  • KDE Frameworks: 5.56.0
  • kf5-config: 1.0