Live TV Only works on the Server Running Mac Mini

Plex Server is installed on a Mac Mini that is always on. I can watch live tv using safari on the mac. It mostly runs OK. Since I started writing this I had one small freeze, otherwise it continues to run. The Mac Mini is connected to my TV so not being able to go full screen makes this a less attractive way of watching.
I’d like to use the Apple TV however that won’t play live TV. It either starts playing it and then quickly stops, or it just won’t play at all. Sometimes it returns a message saying weak signal. Sometimes I get a message saying something like server won’t start - or failed to start.
It’s a little better on my iPhone. Although it seems to keep buffering - or in other words it will not play for more than a few seconds at a time.
Is there anything I can do?