Possibly relevant to permissions: The uid of this process changed from 'root' in 17.10 (where it works), to 'ubuntu' in 18.04 (where it doesn't work).
ubuntu 4468 17.8 1.2 502716 97352 tty1 Sl+ 08:17 0:01 /usr/bin/python3 /usr/lib/ubiquity/bin/ubiquity gtk_ui
In both cases the Xorg process is running as 'ubuntu'.
Possibly relevant to permissions: The uid of this process changed from 'root' in 17.10 (where it works), to 'ubuntu' in 18.04 (where it doesn't work).
ubuntu 4468 17.8 1.2 502716 97352 tty1 Sl+ 08:17 0:01 /usr/bin/python3 /usr/lib/ ubiquity/ bin/ubiquity gtk_ui
In both cases the Xorg process is running as 'ubuntu'.