Comment 3 for bug 1589006

I was able to downgrade the nvidia packages by first stopping sddm via:

sudo systemctl stop sddm.service

I am running kubuntu though. If you're on Ubuntu it is not sddm but lightdm, I guess.

Then:

sudo apt install {nvidia-opencl-icd-361,nvidia-352,nvidia-361}=361.42-0ubuntu2

And reboot!