Not mentioned in that guide is the firewall rule:
@https://doc.pfsense.org/index.php/IGMP_Proxy:
You also need a firewall rule on the downstream side (typically LAN) that matches/passes this traffic which has the advanced option checked to allow packets with IP Options.
This is different (I think) to the 239.255.255.250:1900 logs you are seeing. Those are probably a server on your LAN trying to announce itself via UPNP.
Steve