No, this isn’t expected behavior. However, based on what you suggest, when you remove the one internet cable, that suggests that device was being used to create the SonosNet network. 

Have you ensured that you’re running the latest version of the controller and firmware? I seem to recall along the way there were some issues with accessing the network data, but thought that had been fixed in a more recent update. In your case, I’d recommend that you submit a system diagnostic within 10 minutes of seeing this issue, 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 network and Sonos system.

Hi Bruce,

I will follow your advise and run through the process again to be sure the problem is still repeatable.

Thank you for the links as I was looking for a phone number to call on this issue.