Created attachment 817106 [details]
sample of scrambled login screen (each time different...)

The KDE login-screen shows scrambled, but the password can be entered and after
hit enter the desktop appears (sometimes scrambled, too, sometimes fine). After
a while it freezes. No keyboard available. The computer is still reachable via
SSH from outside.

The freezing occurs randomly. It once was ok for 7 days without reboot and then
suddenly it froze. Sometimes it happened after 1 day, sometimes after an hour.
In the last tries it froze between immediately and within two hours. The system
is unusable now.

While frozen the fans turn at top speed, it seems lot of CPU is used (can't see
it, because GKrellm display is also frozen...) 

Often, before the complete freeze, it freezes for a short time (30 seconds?),
then shows a message that the desktop effects have been restarted. After that
the desktop effects are disabled, but the rest works - for a while until the
complete freeze. While it works closed windows are still shown in the taskbar.
But clicking at them has no effect. They just stay visible there and don't
disappear until logout or reboot after complete freeze.

Also icons that are placed in the two most right rows of the desktop are moved
after logout/login or reboot. They are mixed with the other icons on the
desktop and are distributed randomly. This does not happen, when there are no
icons in the two most right rows. Then all icons stay where they were also
after logout/in.

This is Opensuse 15.1, KDE 5.12.8, Kernel 4.12.14-lp151.28.13-default, 64 bit
Itel i7 CPU 950 @ 3.07GHz, 24 GB memory
Nvidia GF 107/GeForce GTX 460
driver: or from opensuse repo nvidia_computeG04 or with "the hard way"
NVIDIA-Linux-x86_64-390.129.run directly from Nvidia (both show the same
errors)
Screen size: 1920x1200px (Eizo)

A hardware/cable/etc... defect can be excluded: everything works fine without
the nvidia drivers using nouveau (but nouveau has other problems, so I'd prefer
to be able to run the nvidia drivers)

It is 100% reproducible on my system:
run with nouveau: all fine
install suse rpm: errors occur
de-install rpms: all fine
install nvidia*.run: errors occur

I did the de/re-install several times, always with the same results.