Is the Login handled by a desktop manager? If so, what happens if I install another desktop manager (which one will provide the login?) and how to control which one is used?
Whenever I login it looks like the system switches between desktop managers or something: Sometimes I see a background set some time ago, sometimes with monitors in wrong order (left and right monitor switched), then login shows up, but frozen for some seconds with messed up backgound, then refresh and for example background is fixed, and when I finally login using some desktop manager (e.g. cinnamon) then the display has some other graphical bugs which look like switchting back and forth before the desktop manager is finally loaded. (To be honest: I never had a Ubuntu experience without some graphic bugs every now and then in years)