Not exactly sure when this happened as there was a kernel update last night before I shut down and my machine wouldn't boot this morning. After booting with old kernel 4.4.104-39 I ran zypper up and got another kernel update (sorry, didn't note version) but still couldn't boot.
Kernel 4.4.120-45.1 and both failed to boot. I managed to boot with 4.4.104-39 and switched to nVidia drivers and 4.4.120-45.1 now boots using them instead of nouveau.

I should say that I switched to nouveau originally because plasma seemed to keep locking up on me (clock freezing etc.) and, since I don't really play games in Linux, I reverted to the nouveau driver as a back stop and it's been fine up until this latest kernel update.

This is a dual boot (Windoze 10 and openSUSE Leap 42.3) system - AMD Ryzen 5 160 3.6GHzwith 16Gb Ram and NVidia GeForce GTX 970