While 2 of my 3 ChromeCast are wired too, none of those is “wireless” as they are connected to WiFi bridges. I’m also pretty sure to never have seen settings in their configuration to enable wired network or disable WiFi - they are pretty much auto-configuring them self and thus may fall-back to use WiFi if something is wrong / not working on the USB to Ethernet adapter. As Rebeka wrote, Roon is just showing the ChromeCasts advertised on your network. The advertising is done by the ChromeCasts. So it looks like something is wrong with your ChromeCast specifically or your network. Have a read trough this older thread to get some ideas how you possibly can further troubleshoot your issue: