Home Sharing/Big Sur

I've got an iMac running the latest 'Big Sur' public beta, and I've got a couple of Apple TV's. I'm not sure at exactly which point this happened, but I've lost the ability to use Home Sharing.

I've tried logging my accounts on/off the Apple TV's.

I can AirPlay from the iMac to the Apple TV's and play either video or music.

If I use the 'Computers' App on the Apple TV, I can see the music and video, but I can't play it. Music gives no error message, it just doesn't start. Video gives some generic message (Away from home right now) indicating it can't play the video.

If I use the Music app on the Apple TV, I can play my library fine.

Any ideas on this?
Home Sharing/Big Sur
 
 
Q