After Feb 24 update my X11/KDE stopped working (can't log in). (using debian testing)

[Karel Gardas]

Hello,

I'm using debian testing so not sure if this is the right ML, but after 
Feb 24 update I'm no longer capable of logging into the X11/KDE-plasma. 
I simply log into, seeing KDE progress gear and then it returns back to 
login. My .xsession errors shows that KDE complains about connection to 
X server claiming perhaps this died.

Anybody seen this? Is there any procedure how to better debug and report 
such issue?

Thanks!
Karel