Whole sonos system reverted to old Wifi network.

I had the same issue.

Settings → Network → Manage Networks : Delete old networks

You may need to re-register 1 or 2 speakers

This is a real disappointment I'm sure to everybody who's experienced it. For me, a residential integrator who installs systems and manages several hundred homes, some of them with dozens of Sonos's, this bug is something that can take a system which was set up and working perfectly and turn it into one which causes spanning tree issues and your network will flap on and off causing you to drop calls, video meetings, block your internet connectivity all together, and unfortunately for someone like me who runs a business, accrue a whole lot of expenses driving around trying to figure out what the problem is.... Finding that Sonos has reverted a setting which was set specifically in their software, which makes us and Sonos look like jerks in addition to causing the frustration on the part of the owner.

If you guys at Sonos can't fix your spanning tree issues you at least need to fix your Wi-Fi setup so it doesn't revert to a broken POS. 

Normally I wouldn't be so hostile, but I am driving back from a half wasted Saturday trying to fix this for a client whose network went down in the middle of a VC call yesterday because of you. Reputations have to be tended, and you may have a big market share but you're slacking. From my perspective your product is a gamble.

Fix It

Maybe Starlink WiFi went down briefly and since the former WiFi was still defined, SONOS switched back to the old WiFi.

On my system there are two WiFi’s. One set is actually a mesh. All are on the same subnet. The SONOS system is free to use either WiFi and there can be a mix. (Meaning some SONOS units are using ‘A’ while others are using ‘B’.) If one WiFi goes down, all of the SONOS units will switch to the still operating access points. And the SONOS units are free to use 2.4 or 5GHz as they like.

If there is a risk that a SONOS unit could use the wrong WiFi, be sure to remove this network from the SONOS network settings.

Did you supply any data to Sonos so they could figure out what had occurred, and ‘fix it’ for you? Or are you just complaining randomly on a forum, without any data to back up your complaint?

Thanks Bruce. I am complaining, yes.

As it turns out, these forums tend to get more attention from customer service and engineering then actually trying to electronically submit anything and get it fixed. That said, this is something that we have seen happening on several systems and there is most certainly a pattern. Unfortunately due to the nature of having to fix problems with other people's systems in a timely manner, we are not able to sit and wait for Sonos to use our time and our clients systems as a debugging venue. The spanning tree problem is something that Sonos has never addressed adequately since the inception of their devices riding on people's networks and not using zp net. Real facts. 

If it makes you feel better I most certainly can submit system diagnostics the next time this issue pops up as it most certainly will, but given how long this has been problem for Sonos I would not expect anything until people really start complaining and/or choosing other better options. 

Spanning trees are obviously only relevant when in SonosNet mode, and instability is more likely to arise where multiple units are wired. Basically, Sonos’ modified STP can get into a tussle with whatever’s running in the backbone. The latter could well be the more modern RSTP, and the differences in path costs, convergence times, and so forth between STP and RSTP can result in unintended consequences. 

IMO we’re unlikely to see much, if any, attention given to this area by Sonos. The latest Era units can’t use SonosNet at all, and this is a trend that’s likely to continue. SonosNet was essential in its day, but its bandwidth is low and its performance is now well and truly eclipsed by modern WiFi 6 meshes. In fact Sonos is most likely to ring-fence the SonosNet code and post a warning sign at the entrance, for fear of causing regression. 

It would make me feel better. Simply a complaint, especially as Sonos could be having difficulty replicating this issue internally, might be helpful. It’s also a pretty random, and extremely rare bug, based on what I see in this thread. I’ve certainly never experienced it, but then I’m a single point of reference, and only deal with three systems at most. Providing data to an engineer works wonders. I’ve often asked my engineering staff to fix a bug, and the first response is, ‘ how do I replicate the issue’. 
 

Given the infrequency of this, and the movement away from SonosNet, I do agree with @ratty , it seems, especially lacking any replication data, for it to get any significant attention, even given the rant you’ve posted. 

True, somewhat, although this is not just a Sonosnet issue. If it was then it wouldn't cause spanning tree on the lan WHEN THE WIFI ENABLE/DISABLE SETTING RANDOMLY REVERTS TO ENABLED which is not something I can advise on how to replicate but assuming Sonos has a lab with hundreds of devices and people paid to use it, they would be able to catch it. 

And this is not infrequent, I've got 3 systems in the past 3 weeks running on updated and managed networks that have reverted on their own, but since stp takes down the WiFi port when the event happens, the network is rendered useless to the end user even if the gateway and some segments are still unblocked. 

I encountered a Ubiquiti update that wrecked STP for SONOS.