Unplug the Arc from power for a couple of minutes and reboot your router. Also be sure that Wi-Fi is enabled under the Arc’s settings in the Sonos app.

If possible, you also might try wiring the Arc directly to your router with an ethernet cable.

Also, check for potential sources of wifi interference near either the Arc or the surrounds (or both) as well. When in surround mode, speakers connect to a “hidden”  5Ghz channel generated by the Arc, and not your own wifi signal. 

I can’t easily reboot my router as I have a few servers connected that need to stay on wherever possible. However I can see in DHCP that they have been allocated a local IP so can’t see what else rebooting the router might help?

Appreciate that you’re trying to help but ethernet isn’t possible, and I feel slightly bemused that they’d ship with WiFi functionality only to recommend Ethernet when it then goes wrong.

@Airgetlam There’s nothing that should be causing any WiFi interference with surround that isn’t connecting to the system. If anything the one that does connect is more likely to have interference as the sub sits between it and the arc. But, like I say, that’s working fine and the faulty surround is in perfect line of sight with nothing between.

You might try switching the left and right surround speakers and see if that makes a difference.

@GuitarSuperstar 

Is this what you mean or is there somewhere else I should enable it? 

Yes, that is the correct setting.

You might try switching the left and right surround speakers and see if that makes a difference.

@GuitarSuperstar

i think this has come down to the speakers appearing in different groups. I can’t find how to manually add the rogue SL One to the group containing all other speakers.

How do you go about switching the speakers? I’m not quite sure what you mean? They’re either off, or connected…?

Unbond (or remove) the two One SLs as surrounds from the Arc in the Sonos app. Unplug the Arc from power for a couple of minutes and reboot you router. Plug the Arc back in and allow it to reconnect to WiFi, and then add the right One SL as the left surround and the left One SL as the right surround to the Arc. Of course this would mean you would need to switch the speaker positions too.

So for an hour is been receiving this:

However for some inexplicable reason it has finally worked and added the surround to the correct group and connected it.

I’ve no idea how or why this worked so anyone else coming to this thread for advice on how I got this working, I’m afraid this isn’t much help.

I have to say, the app is terrible for troubleshooting. Fine when it all works but hopeless when it doesn’t.