Problem Solved: Interplay of Unifi, Spotify, and Sonos (and Airprint)

I am a dedicated fan of my UniFi Network infrastructure, my Sonos speaker system, and Spotify as a streaming platform. However, Sonos and Spotify did not work reliably within my home. My speakers did not appear in Spotify as Spotify-connect speakers. As Sonos playback had dropouts or latencies. Also, Airprint did not work reliably. 

Forum threads suggested connecting the Sonos speakers to the LAN network. By this, the Sonos speakers start their own dedicated WiFi Network (“Sonosnet”) to communicate with each other. As I have a perfect WiFi infrastructure with my UnFi access points, this solution was not satisfying.

I figured out, my issues had something to do with the multicast traffic/mDNS handling within my network. Although all my devices and access points are in the same VLAN, it seemed that there were some issues regarding the forwarding of multicast packages between different access points and frequency bands. Of course, mDNS traffic was activated within Settings -> Services.

Some users with comparable issues but with devices in different VLANS, could resolve those by enabling Unifi’s “mDNS reflector” (via the Web GUI) or the “mDNS repeater” (a Unifi feature, which can only be activated via editing the config.gateway.json file). However, this approach had no effect for my setup.

The solution: Disable “Wireless Uplink”

Even thoug, it seems like “Wireless Uplink” (connecting two networks only via Wifi) should have no direct effect on mDNS/multicast traffic. However, it has! Disabling wireless uplink in the controller (Settings > Site > Services) resolved all my problems regarding Sonos and Spotify. This seems to be a bug, which should be resolved by Ubiquity.  For me, this workaround is acceptable, as I am not using the Wireless Uplink functionality.