"Multimedia Protocol Policy" in ntopng?

[fvultee]

I have 4 Sonos (home speaker system) on my LAN, all in the same subnet. It's operation after I installed pfSense has been very poor. I checked in ntopng and the Sonos speakers are reporting this:

[16/12/2019 10:38:59][Suspicious Device Protocol] Client protocol "Unknown" is not allowed by the configured Multimedia protocol policy [Flow: 192.168.2.75:45054 ec2-34-229-60-105.comput...:443] [L4 Protocol: TCP]

What the heck is the "Multimedia protocol policy"?

Also it's reporting this:

[16/12/2019 10:42:00][Suspicious Device Protocol] Client protocol "SSDP" is not allowed by the configured Multimedia protocol policy [Flow: BASEMENT:50489 255.255.255.255:1900] [L4 Protocol: UDP]

To be clear all Sonos IPs are allowed to use all ports (firewall rule only for troubleshooting, though it doesn't help in this case).

Any ideas where to look next?