Mcproxy breaks DHCP

I installed and configured mcproxy to be able to access a Spotify Connect device in my iot net:

protocol IGMPv3;

pinstance proxy1: "br-iot" ==> "br-lan";

Unfortunately, my Wifi devices from my attached Unifi network do not get an IP anymore as soon as mcproxy is running. I can turn in on and off and it is very clear that it only works with mcproxy deactivated.

Requests are still received:

Mon Mar 13 19:57:57 2023 dnsmasq-dhcp[3363]: DHCPDISCOVER(br-lan) 
Mon Mar 13 19:57:57 2023 dnsmasq-dhcp[3363]: DHCPOFFER(br-lan)

And I know it doesn't seem to make sense, but it looks like cable bound devices, that are attached to the same switch as the Unifi access points, still get IPs.

Does anyone have any idea what could be going on here?