Try unplugging the Amp for a couple of minutes. If this doesn’t work, contact Sonos Support:

https://support.sonos.com/s/contact

1/ make sure your Apple TV or other periph is up to date

2/ make sure your smart TV is up to date

3/ reset your modem and make sure your wifi sys is up to date

4/ do the Sonos updates

5/ unplug and replug your amp to reset

Many times, updates simply reset a lot of things in your config. Once all this is done, start working through the entire Sonos app re that theater or group. Make sure your amp light is switched on. Chances are good that you’ll be back in business, and running sweet. 

I just had the same issue  1 hr with my outside tech, to understand the above. My system really rocks some great surround sound again, snd the amp totally works as before. 

Sophisticated systems require tuneups as updates are done. Also suggest Trueplay tuning in this process.

I love my Sonos again!