Multicast SSDP packets not reaching router's minisatip server

I have a minisatip server instance running on my ASUS-AX53U. The server (along with the tuner) works well when I configure the clients to use its IP explicitly. Discovery, however, does not work. SSDP M-SEARCH packets are sent by various clients (e.g. VLC, w_scan_cpp) and reach the router (checked with tcpdump), but I don't see them reaching minisatip instance when running in verbose mode in foreground.

I suspect this is due to the fact that they are multicast packets, and that they are dropped by the kernel because of some reason. I have found multiple topics relating to similar issues (e.g. here ), however, most of them describe how to make the router/bridge forward/pass the multicast packets to other network segments. In my case, the packets should reach the server instance running on the router itself.

I have already tried switching multicast related options in interface settings in LuCI. Any ideas what I might have missed? Perhaps someone faced a similar issue and could paste relevant lines from his config?

The only "easy" thing I can think of, currently, is that the TTL somehow stops the M-SEARCH packet from reaching your minisatip server. Maybe try to add the TTL mangling rule to your firewall and see, if that helps?