So I upgraded to plasma 5.0 before the uploads were completed.
This brought my setup into problems.
Problem: After boot the computer produces only a white screen.
From another computer, using SSH, I can login in to the computer (as 'root'). I do not find error messages in /var/log. After "startx" I get a KDE desktop.
Using this shell login I did a full upgrade to plasma 5.8 (SID).
Could I still be missing packages? How to debug this?
thx for any pointers.