How are these Sonos Amps connected to your router? Are you running a wired connection, with at least one connected to the router with an Ethernet cable, or are they all attempting to connect to the Wi-Fi signal?

It’s a rack with all Ethernet connections. 

Have you force closed, reset, or reinstalled the controller?

I’d also be somewhat interested in what switch, make and model,  they’re connected to. Essentially, is it a managed switch, or an unmanaged switch? They’re all in the same subnet, correct?

Thank you for trying to assist. I got Sonos support on the phone and we determined that the Ethernet cable shouldn’t be plugged into the ATT router directly when using a Google Nest. Once I I passed the router and plugged the main Ethernet line into the Google nest directly, all amps were able to complete set up and the system is working like a champ. Thanks again for your assist.