I had turned IGMP Snooping after learning it can help streamline multicast network traffic. Everything was working great after making the change, and I was pleased that enabling the setting would decrease traffic load on the network with no ill effects. However, the next time I opened Spotify and attempted to connect to my speakers I noticed that they were now missing from the connect list, other devices with Spotify running showed up, but the speakers did not.

Since IGMP Snooping was the only change I had made, I turned it off, re-provisioned the system and the speakers showed back up. Turns out Spotify Connect uses multicast traffic to advertise to all your network devices. Problem solved.