I’m using a Lenovo Y510p which I recently upgraded to Tumbleweed.
Everything worked fine till I tried to connect my second Monitor via the HDMI Port. When the monitor is connected I’m not able to login to KDE anymore.
After entering the login credetionals the openSUSE “progress bar” appears and after half of the progress both screens turn black and I’m dropped to the login screen again.
The same issue appeared when I tried to connect the monitor after the successful login: The screen turned black and I was droped to the login screen again.
Looks like nouveau is crashing.
So installing the proprietary nvidia driver might help, although that can be a bit tedious on Tumbleweed: you need to do it “the hard way”, and you need to reinstall it after certain updates like the kernel. https://en.opensuse.org/SDB:NVIDIA_the_hard_way
Also, the driver does not work with Kernel 4.2.0 yet AFAIK. TW still has 4.1.6, but that will be updated to 4.2.x (with x=1 probably) at some time.
You could also try to disable the “KScreen 2” service in systemsettings5 (“Configure Desktop”)->Startup and Shutdown->Background Service, to see if it’s related to KDE detecting the monitor.
Unless the issue was originally resolved at some time (I never heard that it was, only “that the problem is being worked on”), this sounds very much like what was reported several years ago (openSUSE 12.3?) running KDE4 (IIRC).
There was no resolution at that time.
You just had to disconnect the 2nd monitor either when initially logging in or waking up from suspension.
You could also see the basis for why this was happening, whenever you connected the 2nd monitor, it became your primary display (which also became an issue when connecting to a projector).