What has changed in nvidia proprietary driver packaging in 18.04 Bionic?
Don't use a ppa and don't install manually. Just enable the "restricted" and "universe" repositories and then install the drivers using apt:
sudo apt install nvidia-xxx libcuda1 nvidia-opencl-icd nvidia-settings
Replace "xxx" with the actual driver version.
For a list of available drivers, run the following command:
apt-cache search nvidia | grep -P '^nvidia-'