Just a guess, but it sounds like you/someone may (possibly) have upgraded (accidentally) some of your compatible players from S1 to S2, but that’s only an initial thought on my part.
 

If you go into "Settings/System/About My System” in the Sonos App, it will show you a list of your speakers and their software Version: Perhaps take a look and see if your players are on version 11.x.x.x (S1 devices), or version 12.x.x.x (S2 devices).

Yes. Some are on S2. This could only have happened when I downloaded the desktop app. How I can I set them back to S1?

Richard_8,

I really don’t have any idea how it might have happened. I rarely use that version of the Sonos App myself, so can’t really help explain what you might have done, accidentally.
 

It seems you will have to revert the upgraded devices back though, to S1. I can perhaps assist with that process, that is if you do need any help with that aspect?

Ah I see - yes you can go back to S1, you need a mobile S1 Sonos controller device (iOS or Android) - don’t use a device that runs iOS 14.2 as that Apple version has a few issues, best to use an earlier, or later version of iOS, or any recent compatible Android mobile device. The mobile needs the S1 App only - if S2 is installed then remove that newer App.

1. Make a note which devices are S1/S2 and then Power off all your Sonos speakers.
2. Wire just one S1 only (non upgraded device) to your router and power it up.
3. Open the S1 App and you should see just your wired S1 Sonos product in the App. Ensure your services and playlists are present, before moving to the next step.
4. Do this step one at a time ...Factory reset/Power On your S2 upgraded products, so their status light is flashing green and using the S1 App goto "settings/system/add product” and follow the instructions to add the device to the S1 system - it should downgrade to S1.
5. Repeat for the other previously upgraded Sonos devices.
6. If all is well, then power on your other S1 devices.

You can then put the devices back to where they were and hopefully all will be fine. 

Thanks. I will attempt in the morning. I may well delete the desktop app then - although that used to be the main control outside of the handheld controllers back in the day!

Seems the UI has got worse over the years. Shame - I've been using Sonos for around 11 years now!

Maybe just ‘reset’ the S1 Destop App (DCR) and when you’ve finished the setup tomorrow, you can open the S1 DCR and just choose the option to connect to the ‘existing’ system… it should then work fine. If invited to update to S2, just dismiss that invitation.