I have what may be a similar issue. I mainly use NoMachine to administer my Ubuntu media server from my general use Windows machine. I was having various graphical and other issues with Ubuntu Gnome 16.04.3 and NoMachine, so I rebuilt the system first with Ubuntu 17.10, and then finally with Ubuntu Budgie 17.10. Most of my graphical issues went away, but now I see several entries for my old installs from my NoMachine client on the Windows box. In the past 24 hours, I’ve had 3 different Ubuntu installs on the same hardware, with NoMachine installed on each of them for testing. When my client opens on Windows, I see all 3. They all seem to work, and after some time, the two “phantom” listings seem to go away, but when I started looking for a way to delete these extraneous connections, there doesn’t seem to be a way. Where could the information about my old installs come from?