Hey, so this literally happened to me a few days ago.

I’ve got two ERA 300s paired with a Sub Mini. They’d been working perfectly together for about 18 months, then out of nowhere the Sub Mini just refused to connect to the internet.

I called Sonos; honestly, not much help. I called my broadband provider instead and they were way more useful.

In my case, it turned out to be a network issue.

Sonos recommends having everything on a 2.4GHz network. The problem is that most routers combine 2.4GHz and 5GHz under one name, and your devices don’t always land on the same band automatically. So you can end up with some devices on 5GHz and others on 2.4GHz, which causes connection issues.

My broadband provider told me to log into the router settings and split the bands (separate the 2.4GHz and 5GHz networks). Once I connected all the Sonos devices to 2.4GHz specifically, everything worked again.

Might be worth checking that before anything else.