Not enough information to even be slightly confident about an answer, but if I were to hazard a guess, there’s some oddness going on with your CEC (HDMI ARC) connection. Could be as simple as one of the two devices losing electrical power when you turn the system off, or something more complex. 

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

Unless the product is in the ‘trial’ period, it’s unlikely to be able to be returned. If it is under warranty, it could be replaced/repaired.