How does Spotify Connect usually make the connection to the Atom?
I thought using the “Connect” version of either would communicate using Cast or AirPlay (depending on what system IOS of other phone/tablet you’re using)
No, Connect does not work like that. The device being controlled connects directly to the streaming service. Your phone, tablet, whatever becomes a remote control. Nothing is streamed from phone/tablet directly.
Have you tried powering down from the wall socket your router and Atom and shutting down your phone. Reboot the router before switching on the Atom and phone?
My memory has been jogged. I think this is some sort of conflict between Spotify and Chromecast. Have a look at thread, I think it’s the 15th post that gives instructions to disable chromecast and then Spotify should work. However, not much good if you use chromecast.