I installed KDE Plasma a week ago, tried it and left. Then yesterday I decided to play more seriously with it. I updated it to 5.9 and tried to use it.
It had a lot of problems and took me hours to solve them all. Just to find another issue that wasn’t critical but certainly annoying. But it was too late at night, so I cleaned the computer using Bleachbit and turned it off.
Today I turned it on and everything was working fine, so I assumed that some temporary file, cache or whatever was the cause. I used my computer normally and turned it off when I had to go out. So far so good.
And then it happened again.
Windows seemed to flicker and twinkle, often refusing to disappear when one would close them. Also minimise/maximise caused them to tremble and leave a ghost of window over the desktop. Often I had to click twice or more on the “Show desktop” button to get them to disappear. It was driving me insane when someone from the Fedora Telegram group sent a suggestion to fix it.
The solution to this weird and apparently random problem was quite simple. If you go to System Settings => Display & Monitor => Compositor you’ll find some options including the rendering backend. Set it to OpenGL 3.1 and apply. That should be enough to fix the “bug”. If the problem seems to come back, change the rendering from Accurate to Smooth (or any other that works for you).
Laptop: Dell Latitude E6500, with Nvidia video card, 500GB hard disk, 4GB RAM and Dual Core processor. System: Fedora 25 Workstation with KDE Plasma 5.9.
Hope this is useful, thanks for reading!