I've recently switched from Gnome to KDE (clean install of Kubuntu 18.04). When I start up a game called Factorio (maximised window, not full-screen) the main KDE panel stops refreshing, eg. The clock stops and there are no updates to refresh it. As soon as I exit the game, it starts again. My best guess is that KDE is detecting a game is running, so stops refreshing assuming that it's running full screen, so doesn't need refreshes. I have an Nvidia card with their driver if that has any effect. So, anyway to fix this?
It's a bug, though not necessarily KDE's one. At 27-th comment Thomas — a KWin developer — notes that though the problem is seen at plasmashell, the actual bug is likely either in QtQuick, or in NVidia driver. Given later the whole bugreport got filled with complaints from NVidia users, and at comment 120 someone noted that the problem never occurs with Intel or AMD GPUs, it's almost definitely a problem with their driver.
For what it worth, someone left a comment yesterday:
Hi ! I don't want to get you people excited over nothing but here's an excerpt of the new Nvidia drivers update :
"Fixed a bug that caused kwin OpenGL compositing to crash when launching certain OpenGL applications." (fixed in the 390.77 and 396.45 Nvidia drivers)
You can give it a try.