Poor (weak) wifi, at a first guess. Can you try it in situ connected with a long Ethernet cable and see if that fixes it - or at least helps identify the issue? Are you grouping living room and office, or them plus bedroom? Does it help doing both/all 3 rooms? 

So the symfonisk is actually the furthest away from the Beam so I don’t think that’s it. They connect easily. Like I said, it sounds like it’s rotating through sound, not buffering.

It doesn’t help with all 3 rooms but the symfonisk still works hmmm

I’ll to capture the audio on a quick video and add that for reference. Only happens when the source is the Apple TV. Streaming on all 4 works great, record player hooked up to Five works great on all 4, too 

Remember, the signal from the TV is much ‘fatter’ than a normal music stream, and it could be just enough to be causing wifi interference only when you’re grouping the TV input on the Beam. 

I would certainly be a fan of @nik9669a ‘s test case. 

Am I connecting the Beam to ethernet or the Five? 

It works!!! Plugged Ethernet into Beam! Y’all are the best! Been dealing with this for years lol