I have similar issues with Plasma and definetly can say it is a graphics card/hardware problem which is intertwined with the graphics driver. Plasma is very hea

I have similar issues with Plasma and definetly can say it is a graphics card/hardware problem which is intertwined with the graphics driver. Plasma is very heavy on graphics effects. You might want to change details (like having shadows or transparency) in the settings to see if it changes something.