SUMMARY I used to be able to "place" my laptop monitor and vga connected monitor relative to each other. This does not work at the moment. STEPS TO REPRODUCE 1. open kscreen kcm module in system settings OBSERVED RESULT only external (VGA) monitor is shown EXPECTED RESULT all monitors (including laptop monitor) are shown SOFTWARE/OS VERSIONS Linux/KDE Plasma: kde-neon / 5.0.0-27-generic KDE Plasma Version: 5.16.5 KDE Frameworks Version: 5.61.0 Qt Version: 5.12.3 xserver-xorg: 1:7.7+19ubuntu7.1 ADDITIONAL INFORMATION If I unplug VGA monitor no monitor is shown at all. My monitor setup still works otherwise: from time to time I change to a different desk with a different external monitor that is placed at the other side of my laptop and the placement of this monitor is set correctly. I don't know which software change contained this bug because I didn't change my monitor settings for several months.
I just learned that this only happens if the external monitor is connected before login. If I connect it after login both monitors are shown correctly.
This should be fixed in Plasma 5.17, where the KScreen KCM was rewritten. I was just testing this use case yesterday and it works great now!