KDE just gets total confused when I connect or disconnect a new display, windows jump all over the place, sometimes they move out of the visible screen area if I switch between hiDPI and non-hiDPI displays, or even just disconnect and then reconnect a UHD monitor. I've seen some reports pointing fingers at Qt as the main culprit, tbh I don't care, it doesn't work for the end user.
The latest Ubuntu on Gnome at least doesn't get confused, but it does not recognize my monitor sometimes (I have to turn it off then on again, for example when waking up from suspend), and switching between displays takes about 20-30 seconds (I have my laptop screen disabled if a monitor is connected). But it doesn't remember my open windows, nor the past position of my terminal, which is set to auto-exec on login. This is something that works much better in KDE.