The LTS upgrade from Ubuntu 16.04 to 18.04 has largely gone smoothly.
Once again there are problems on the VNC side (logging in remotely, using VNC), particularly useful when accessing the server from an Mac (OSX) machine, where you “share screen…” with the Linux server. However, it appears that the upgrade to Ubuntu 18.04 probably changes the default desktop back to gdm3, which still appears not to support the VNC setup well according to the below:
https://askubuntu.com/questions/1033274/ubuntu-18-04-connect-to-login-screen-over-vnc/
Running the below command, and selecting to use lightdm as the desktop manager will get things back working again.
dpkg-reconfigure lightdm
It appears this changes the following symlink:
root@shuttle:/etc/systemd/system/multi-user.target.wants# ls -l /etc/systemd/system/display-manager.service
lrwxrwxrwx 1 root root 35 Dec 26 21:44 /etc/systemd/system/display-manager.service -> /lib/systemd/system/lightdm.service