External monitor will not wake up after docking

[cz0]

Hi, folks!
I'm having a wired problem with an external monitor connected to docking station. I found, that in different scenarios external monitor behaves different:
1. if laptop booted connected to the docking station, the external monitor will be on (mirroring laptop's screen) from the system power on and will work all the time including soft (DPMS) sleeps on system inactivates;
2. if I undock laptop and then dock it back again to the station, external monitor will not wake up from sleep;
3. forcing DPMS through power cycle by running 'xset dpms force off; xset dpms force on' will wake external monitor on and it will work as expected until next undocking;
4. if I switch to text console after docking with external monitor been on sleep mode it will wake up and continue to work as expected after I switch back to X (KDE in my case);
5. login out from a running KDE session to SDDM after docking will bring external monitor on again (dew to brief switch to text console, I believe)
6. going through soft sleep (S3 sleep) of the whole machine after docking will wake up external monitor from sleep;

I have no any additional monitor definition in my Xorg.conf and KDE is not aware of second monitor as well (no corresponding settings in System Settings, I have no idea how to get them). I'm running dynamic Xorg configuration.

This is xrand output when both monitors are ON: