Broadcast to 239.255.255.250 isn't working?

[Phoenix7351]

This is driving me crazy. I'm trying to build a network scanner--including finding UPnP devices. I have tried SwiftSSDP and other libraries and I'm getting back nothing even though I know I have PnP devices on my network (I can broadcast from my laptop, for instance, and get responses).

The irritating this is, I'm watching traffic on Wireshark, and never seeing a broadcast from my phone to 239.255.255.250. Again, broadcasting from my laptop I can see this broadcast.

I have gone so far as to manually try implementing SSDP myself through CocoaAsyncSocket. If I broadcast to 255.255.255.255, I can see the packet, but I don't get a response (obviously because SSDP protocol is listening on 255.255.255.255). If I broadcast to 239.255.255.250, as SwiftSSDP is rightly doing, no packet shows up.

Is SwiftSSDP still working for everyone else?