Igmpproxy Turris 6.0

I had the same problem.
As a workaround I installed and enabled udpxy and disabled igmpproxy.
I then manually activated/added the IGMP rules in the firewall:

config rule
	option name 'Allow-IGMP'
	option src 'wan'
	option proto 'igmp'
	option family 'ipv4'
	option target 'ACCEPT'
	option enabled '1'

config rule
	option name 'Allow-Multicast'
	option src 'wan'
	option proto 'udp'
	option family 'ipv4'
	option dest_ip '224.0.0.0/4'
	option target 'ACCEPT'
	option enabled '1'

I was lucky, since I use with “IPTV Simple Client” on KODI. It has is an option to add the IP address of your udpxy server, and that’s all it needs.