Setup: 
internal laptop screen (eDP1)
two external displays (DP2-1 and DP2-2) connected via OneLink Pro docking station with Plasma shell panel on the DP2-1 (as a primary display)

KScreen works correctly when docking station is connected - both external displays are turned on, panel is properly moved to DP2-1 display (see http://rezza.hofyland.cz/kde/kscreen.log.1). When docking station is disconnected, nothing happens. Cursor stays on the external display, same as for panel and windows (see http://rezza.hofyland.cz/kde/kscreen.log.2). When I connect docking station again, nothing happens either. Without docking station, it's possible to run xrandr without any command line option and it properly moves panel to internal screen, same for windows (see http://rezza.hofyland.cz/kde/kscreen.log.3).

I can provide more details if needed. Just a note - it works in other X11 based DEs (aka GNOME Shell) on Fedora 25 and it worked before in 5.7 release. And KScreen is aware of the change as the new kscreen.log is created.

 

Reproducible: Always

Steps to Reproduce:
1. docking station with two external displays connected
2. disconnect docking station

Actual Results:  
Configuration change is not reflected, panel and windows stays on the second screen until xrandr command is executed.

Expected Results:  
Configuration change is properly reflected when docking station is disconnected without the need to type xrandr command.