Best answer by Airgetlam
But before you go that far, I'd try a simple factory reset of only that speaker, and then re-adding it to your system. If that doesn't change the behaviour, wire it up so it shows in the controller app, and submit a system diagnostic, and contact Sonos Support to discuss it. I tend to suggest the phone folks, they have more tools available, but are only available during business hours. Both the Twitter and Facebook support folks are available 24/7.