blackscreen after login

[cluster]

I use the latest & up2date Kubuntu 18.10 (lowlatency) after an update yesterday and the day before the desktop turns black (blackscreen) after login.
The original desktop is shown for two seconds & it seems when KDE build up the taskbar the screen turns black ... I can see the mousepointer but nothing else.
I have alredy tried to re-name .config & .local folder but it does not change anything ... how can I fix that issue?

[cluster]

it seems the freezig is back since tatest upgrade ... mouse pointer freezes or better the complete system freezes again after working well for about 7 months ...