I have had surround sound set up and working in conjunction with my Arc and Sub for 10 months. Over the last few days it has stopped working. My app is up to date, all my equipment is up to date. I have reset and rebooted both Sonos 1 speakers. I have rebooted my wifi (nothing else has a problem with wifi). I get two messages, depending on where I am in the rebooting process:

There was a problem adding your surrounds. Check the network connection and make sure your products are powered on (done)

Your left surround is unavailable. You can add a new surround or remove the existing one (have tried both).

The Arc, and both Sonos 1 speakers all work independently of each other, just not as a surround.

Please help!