Hi @ddupre.
Thanks for reaching out and welcome to the community!
I appreciate your detailed post outlining the issue as well as the step(s) that you did, let me help and try to figure this out.
In order for Sonos products and controllers to associate with each other, the network must pass Unicast, Broadcast, and Multicast packets. If any of these types of transmissions are interrupted or not forwarded correctly across third party devices, this association will fail.
To better understand, kindly submit a diagnostic report through the Sonos app, using the working controller and another one using the controller that experiences the issue, then reply with the confirmation number. I'd start by reviewing your system, it will help in identifying what's possibly causing the issue.
I’m looking forward to assisting you further from here.
If you have any other questions or run into any issues, please do not hesitate to reach out, we are always here to help.
I am passing all the protocols. Like I said, the system has been working fine for months with the S2 controller and many years with the previous controller. It’s now been working again for a day or so. I think what happened is that my Unifi switches had a firmware update a couple of months ago, and it changed spanning tree to RSTP instead of STP without my knowledge. Sonos does not support RSTP, but it seemed to work for several weeks anyway. Only recently did things start getting strange. After changing my switches to back to STP and rebooting everything, I now see all players.
What is most interesting about this is that my 8 Sonos players are all wireless. Nothing is wired, so it’s odd that RSTP or STP would make a difference since both of those services are designed to prevent loops with wired or multiple connections. All players continued to work. It’s just that SOME Controllers didn’t see them. I wonder if something else was going on. Maybe the fix was more about me restarting the switches vs. putting STP back on.
Does the Sonos controller expect a static connection to a single access point? I have 3 access points in my house. When they provision or lose power, Sonos players will connect to another one. For any other client, it shouldn’t matter, but I’m not sure if Sonos is doing anything funny on its own. I can imagine some trickery to handle grouping players and keeping everything synced.