Probably it’s igmp snoop, which kind of a protocol violation. It’s understandable because multicast over WiFi is really a problem, especially if you’re transmitting a TV stream, but if the snoop implementation is poor or out of date you’ll end up breaking anything based on mDNS/Bonjour, so pretty much Apple build the last decade, and it’s difficult to diagnose.

If you have TV based on multicast, put it on a separate VLAN so it doesn’t end up spreading over your whole lan.

Do you happen to have any resources/tools/ideas on how to troubleshoot this? I’m having issues with mDNS sometimes just not working on a network I maintain. I can run Wireshark on two devices and see that one is sending out mDNS queries and the other isn’t receiving them at all.

It’s not just mDNS though; all multicast traffic is affected (sometimes ARP doesn’t even work, and I can’t ping the other device by IP).

I've had an issue where mdns transmit would cease after X minutes uptime on windows. Nothing even shows up in Wireshark. I'm still not sure why but I'm assuming the NIC driver for windows didn't like it. Switching from wifi to ethernet fixed the problem. Switching to Linux (same machine) also fixed the problem.

Oh and it was only certain multicast udp that was affected. Regular ip broadcast still worked.

ARP is not multicast in the IGMP sense, if that doesn’t work your cabling or switches are broken or you have a serious firewall issue. But given it sometimes doesn’t work, probably hardware.