After upgrading to 4.11, the login from KDM just returns back to KDM. (At first the system would bring up the desktop background, a mostly frozen system and a Dialog with the message that Kwin crashed multiple times, eventually it just wont get past KDM.) When I create a fresh user directory with just skel then I can login into KDE which will of course not have any of my settings and menus. It will have desktop effects. The problem isnt video drivers or xorg.