This problem occurs since a few weeks: After installing a new kernel (4.18.8-1-default right now), the NVIDIA module (nvidia-uvm-gfxG03-kmp-default-340) didn't get updated/created for the new kernel so it couldn't be loaded after reboot.

My "quick solution" was to remove and then reinstall the NVIDIA packages:

zypper remove nvidia-gfxG03-kmp-default nvidia-glG03 x11-video-nvidiaG03
zypper install nvidia-gfxG03-kmp-default nvidia-glG03 x11-video-nvidiaG03