So it looks like there was an issue with a previous update which broke the guide for shared users. I’ve just been asked to update the server and it seems to be working alright now. I just checked the Plex Media Server Announcements and StSimm1 has said
Plex Media Server 1.18.1.2019 is now available to everyone
FIXES:
• (LiveTV) Hubs and Grid may not load for shared users (or may take a long time to do so)
Hopefully the Live TV guide continues to function correctly. I will update this post if anything changes but so far this update 1.18.1.2019 seems to fix the issue.