Try rebooting your phone and PC. Also try deleting and re-installing the Sonos app.

I tried already to restart and to reinstall the application but still the same.

Try unplugging the speakers for a couple of minutes and rebooting your router.

I did that too 

Someone above mentioned delete and re-add the app. You mentioned that you restarted and re-added the application. If you didn’t actually delete the app (not just closing it but deleting it), try that. 

The next time you post a question it would be nice to state the things you already tried…..

I’ve read some posts and this is what I already did:

• delete and reinstall the phone application;
• delete and reinstall the windows application;
• unplug and replug the speakers;
• reboot the internet/router box.

What is still working:

• all physical functionalities (sound out, speaker buttons);
• all incoming commands (from sonos apps, api, through hdmi-cec);

What is not working:

• all outcoming information not available in sonos apps and api (volume shown at 0, activity is displayed like “no selected music” even sound comes from tv, ...)

Thank you for any help.

Hi @dakim 

Welcome to the Sonos Community!

This sounds like a communication issue between the Sonos app and the rest of the Sonos system. I recommend you get in touch with our technical support team, who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports. My suspicion is that it has something to do with the network topology - perhaps you are using unsupported WiFi extenders?

I hope this helps.