Have the same issue as well with a 750ti. Ran sudo eopkg up and checked for broken packages. Also tried rollback to previous up date which didn't work either. Running sudo eopkg remove nvidia-glx-driver-common worked to bring back to a working login screen. This PC also duel-boots with windows and uses uefi.
Then I checked uname -r and it was back on the lts kernel. So I reinstalled the nvidia drivers, pressed esc on boot and picked the last kernel which worked, which makes it the same solution to last breakage. Updated the clear boot manager, but the change didn't stick after reboot.