I use my laptop either with two external screens connected to a docking station while the laptop screen is disabled (lid is closed) or only on laptop screen.

When I remove the computer from the docking (thus the external screens are disconnected) while the screen is locked and after this I open the lid, the screen is black, only the mouse pointer is visible (it can be moved) and the screen cannot be unlocked. The only way to unlock the screen is to go to a terminal screen and issue 

loginctl unlock-sessions

After this the screen is back and everything works normal. This seems to be a major issue, since the user is practically locked out of the computer, and for most users the only solution is hard reset.

This also happens when I suspend the laptop with the screens connected and resume it after removing it from the docking.

In some cases I even cannot switch to the terminal screen.

This bug appeared in 5.8.5. Maybe it is connected to bug 371734 and it's fix. I guessed it is a multiscreen issue rather than kscreenlocker.

My system is Opensuse Tumbleweed, Plasma 5.8.5, Frameworks 5.29.0, Qt 5.7.1, kernel 4.9.3 64bit