Comment # 7 on bug 997294 from Wolfgang Bauer

(In reply to Vladyslav Hnatiuk from comment #6)
> (In reply to Wolfgang Bauer from comment #5)
> Plasma started at all always, but when I use sddm, I should open console
> mode(ctrl+alt+f1), then again graphical(ctrl+alt+f7) and plasma workspace
> appears active.

So it does start "in the background", only the screen is not updated?
Would rather sound like a graphics driver problem then I think.

Which graphics driver are you using? Is that the same on all affected systems?
Does booting with "nomodeset" help?

> Should I make new log from sddm boot?

I don't think that would help in this case.