Comment # 11 on bug 997503 from Rich Coe

I have reproduced the problem without kde, I used lxqt.

After suspend/undock/resume, the LVDS is blank. 
I can switch to fb1 and login, but I can't make the display show up
on fb7.  The removing power cord and attaching it trick doesn't work.
I started another xserver, it ran as :1 on fb1 and that didn't make a
difference, but I didn't think it would.
If I re-dock, the displays show up again on DP-1 and DP-2.

I tried 
xrandr --output LVDS-1 --primary --auto
and other xrandr commands, but it didn't change anything.
I may have not done it correctly though.

I will switch to lxqt again and try another xrandr command again.