The autohide function for the bottom default panel flickers and has been (for me) for a month or two since using ~5.10.4. Currently on Kubuntu artful and the kubuntu-ci/stable plasma desperately trying to get to a version where there is no autohide flickering. It's hard to describe the problem so here is a video example... https://markc.blog/public/20171015_Plasma_Panel_Flicker.mp4
I can back this up. This has been happening to me since I started using autohide. It's pretty annoying. I'm on 5.12, but it happened on 5.10 and 5.11 as well.
Created attachment 110910 [details] Video of flickering
Good to know I am not the only one. I'm also still getting this flickering on 5.12 but perhaps not quite as bad recently. Sorry about removing the video from the link in my original post. I've just updated it with a new one so ignore the date in the filename, it's really done on 20180223.
Related bug https://bugs.kde.org/show_bug.cgi?id=376065
Cannot reproduce in Plasma 5.21. Can you?
This has not been a problem for me for at least 2 years now. Actually, since I switched to Manjaro.