I spent three to four hours on the phone with SONOS trying to solve this to no avail, but managed to finally solve it myself.
The symptom: All speakers play SiriusXM simultaneously just fine (I have seven rooms with a 5.1 setup, 2.1 setup, playbar and sub, play 5, and the rest are a single play 1), but if I use Spotify, Tidal, Amazon Music, etc the speakers in different rooms would cut out and come back at random. Even different components in the same room, for instance a rear speaker or sub might drop in my 5.1 room then come back, or a L/R speaker in a stereo set. If I kept the groupings to a minimum, for instance two rooms, things seemed to work okay. Once I got above that, things would go to hell. Also, this is a two story 1400 sqft townhome with a brand new top-of-the-line $400 Netgear router with gigabit internet. I get about 800mbps on my iPhone as far away from the router as I can get in the house. Before this, I was in a one-story 900sqft place and was only using speakers in five rooms... same router and internet, same issue.
The critical information: I moved. I moved and am using the same router, but I changed which speakers were in which rooms.
SONOS support’s answer: Interference. We changed channels, ran eithernet cables, changed the main controller speaker... no help. They spent three hours with me and had no idea.
The solution: After you move, even if you use the same router, reset your controller and manually reset the first speaker you add before setting up your SONOS system again. Once that speaker (I used my Playbase) has the flashing green light, create a new SONOS setup in the app. From there, you can add all the other speakers without doing the hard reset for each speaker. It sounds awful, but it’s not all that bad and it actually works. You can reset the controller in the app. To factory reset speakers, just plug them in while holding the pair button or volume up and play/pause simultaneously depending on the device until the light alternately flashes white and orange.
This whole process is basically the ctrl+alt+delete for SONOS.
I don’t know why this happened in the first place and told support “SiriusXM works fine, so it isn’t interference” but they seem to focus on wireless connectivity issues when you call them. If you’re in a situation like I was, do yourself a favor and start from scratch. It’ll be faster than the 30+ min hold time and wireless troubleshooting process you’ll go through with a technician.
Hope this helps someone!