I’m not sure if this has been discussed already. A few days ago I lost the connection to Sonos on my smart phone.. I restarted the router, and things came back online but then it disappeared again.
If this has happened to you check your Wi-Fi settings on your phone make sure it’s the same as the Wi-Fi setting at your router.
every now and then mine switches to the smart phone instead of the router. I hope this helps someone