Firstly what model/versions are the phones you are using and which operating systems are on those devices - does everything in your setup meet these system requirements:

Sonos System Requirements:

https://support.sonos.com/s/article/126

S1/S2 Controller App Requirements:

https://support.sonos.com/s/article/4875

Have you checked the Sonos App “Settings/System/System Updates” for any App and/or firmware updates?

What type of WiFi system is in use? Is it a centrally based router with/without any other access points or a mesh system?

What, if any, Sonos devices are wired to the network and to what are they actually connected, router, switch (managed, or unmanaged) etc?

Thanks very much for replying so quickly.

My Sonos is up to date.  I just checked now and there's nothing available.  I did install an update prior to the problem occurring, but I'm not sure how long before the update it was.

I am using an iPhone 12 with iOS 15.1, a Samsung A70 on Android 11, MacOs Monterey 12.0.1 (but problem also occurred on Big Sur).  As far as I can tell everything is as up to date as it can be, and certainly meets requirements.

The router is a normal vodafone broadband router.  There are no switches connected to it.  No mesh or any other access points.  We did have a wifi extender that's been connected for ages, but we just switched it off in case and all looks the same.

I have one Sonos One plugged into the router, and the rest use wifi.  The actual sound is pretty solid - I usually have all speakers playing in a single group and it's been working well.

I'm reasonably sure that the Sonos is setup to use my wifi network rather than the Sonos specific network.  I'm not 100% sure how to check from the settings.  However, I have had experience of wifi interference in the past which cause sound dropouts, skipped tracks and that kind of thing.  I'm not really getting anything like that now - only controller problems which is a new thing.
 

I would first set your routers 2.4ghz channel to use either channel 1, 6 or 11 and set the SonosNet channel in The App ‘Settings/System/Network’ so it’s at least 5 channels away from your chosen router channel. So just as an example, if you were to set your router to channel 6, then set your SonosNet signal to use either channel 1 or 11. 

If your router uses Airtime Fairness or QOS then switch off those features.

Reboot your router and the wired Sonos One and perhaps also just check the Ethernet cable between the router and your speaker.

Then just reboot reboot your other ‘wireless’ Sonos devices starting with the nearest and the next nearest to the router and see if that fixes the issue.

If all does work, and you do not have any battery powered (portable) Sonos devices (Move or Roam), I would also then go back to the Sonos App ‘Settings/System/Network/Manage Networks’ select your router WiFi SSID in the ‘previously used’ networks list and choose the option to remove it. The WiFi credentials are not required when using a device wired to your router.

Hope that sorts things for you.

How do I check if the Sonos is currently using my wifi network or its own?  Sorry if it’s a stupid question - I had a look and the network options all seemed to be about changing it rather than telling me how things are currently setup.

I’m a little nervous about changing the wifi settings.  When I first switched to Vodafone last Christmas I had all sorts of problems with wifi and Sonos.  In February I even bought another router - which was much worse so I returned it.  But then from, March maybe, it has somehow been absolutely fine.  So I want to make sure if I meddle with my wifi settings that I can switch it back.  Although the controllers are all broken, actual playback is working very well.  I’d rather this scenario than the controllers being fine and the playback all over the place.

If you goto the Sonos App ‘Settings/System/About my System’ you will see your devices listed .. next to each device is a Wireless Mode WM: 

• In SonosNet (wired) mode the speakers and any surrounds are set to WM:0
• In WiFi mode normal speakers (not surrounds) are set to WM:1
• In WiFi mode surrounds/sub are set to WM:2

It is often helpful to set the WiFi Channel to a non-overlapping channel - 1, 6 or 11 and the SonosNet channel so that it’s 5 channels away from the chosen router channel. Also remove the WiFi credentials (as mentioned) from the App, that’s if all devices are showing as WM:0 (SonosNet) which they should be from your description. 

Note too, that it’s worth ensuring that your Sonos One wired to the router is at least 1 metre away from the router, to reduce the potential for interference. 

You perhaps could also try your mobile devices either on the routers 2.4Ghz band or the 5Ghz band to see which works best for you… if using the 2.4Ghz band, then try setting the channel-width to 20MHz only, if your router allows that, as that too can often improve things.

HTH.

Ah, thanks.  I checked and everything is WM:0.  I’m not sure this was intentional on my part, but must have happened when I switched back to my Vodafone router and is probably why things started to work better.  Historically I’ve had more success in the other mode, but maybe that’s because my BT router had a stronger wifi signal.

Anyway, we had a power cut before I had a chance to change the channel settings, and now I’ve brought everything back up again the controllers seem to have started to work.  So I’ll wait and see what happens before changing anything.

If it was a wifi interference issue, would I not have had playback issues as well?

Anyway, thanks for your help so far - I will try your suggestions if the problem comeback again.

Without being too technical, I think it’s more to do with the controller devices discovering the speakers, rather than it being an issue with them actually dropping from your network - Sonos uses SSDP multicasting to discover the devices and so my thoughts were to setup your system with the potential of it having less opportunity for WiFi interference and so by having the setup I described, it might assist things to communicate in a much better way - but if it works now, then I guess that’s it - no point trying to fix it, if it’s not broke.

One thing I would do however is to remove your WiFi credentials from the App network settings as I described earlier - it reduces the slight opportunity of your speakers alternating between a SonosNet signal and your WiFi signal, as that, by itself, ‘may’ cause the issues you were seeing.

OK, thanks - that’s interesting.  I’ve removed my wifi network password using the app as you suggest.  I’ll see how it goes this week.  Again, really appreciate the help.