Performance drop when resizing windows on X11 Plasma 6

After upgrading to plasma 6 on x11, fps drops when changing the window size. At the same time, it was noted in the system monitor that when the window size is changed, one processor core is loaded up to 50%. This issue is visible when live desktop wallpaper (wallpaper engine or Smart Video Wallpaper) is enabled. But at the same time, this problem does not exist in the Wayland session. Before the update everything worked well. What could be the problem?

Do you have an NVIDIA GPU and are you using the panel in its default “floating” configuration?

Yes, I use NVIDIA GPU. I also use two panels. And they are both floating. One panel is static and the other is auto-hide

Does the issue go away if you make all panels non-floating and opaque in the panel settings dialog?

The problem remains even with opacity and non-floating panels

I noticed that when changing the window size, kwin_x11 loads proccessor by 47%

Unfortunately that is a longtime NVIDIA driver issue. There isn’t anything we can do about it I’m afraid. NVIDIA just needs to fix it themselves. In the meantime you can use the Nouveau drivers if you don’t need gaming-level performance, or you replace your GPU with one from AMD or Intel.