Gonna split this up into it's own dedicated thread for better SEO. I'm almost certain Bionic is still using systemctl. So you don't have to run "service". To get this working, SSH into your machine, and run:
sudo systemctl disable logitechmediaserver
Make sure your LMS have all the necessary dependicies by running the following:
sudo apt install -f
next, reboot the Snakeoil PC.
Now login to the Snakeoil webApp. You should still see LogitechMediaServer as one of the media players. Make sure this option is selected. If you are only using LMS as a server, uncheck the client box. Now hit Save.
Wait for the players to load. And you should see at the top that the LMS is loaded (it'll show you a PID), or errored out (red error text).
If these steps don't work, click on the red error text and let me know what it says.