I updated my system from kde-plasma 5.4.2 to 5.4.3, kde-frameworks from 5.15 to 5.16, kde-apps from 15.08.2 to 15.08.3, and now my KDE desktop crash on start and kick me back to SDDM. From clear new user desktop start successfully.

I need a normal desktop start from my old user! I don't want to re-customize my desktop!

Problem solved by:

rm -r ~/.config/plasma-workspace