IPTV IGMP Proxy - Working but stuttering

mirkwoody

The story:
So I wanted to setup Pfsense for my parents, since I had great joy with it the last many years. Their ISP is the same as mine, but they also got IPTV in their package. Provided over a fiber connection.
It's the first time I ever did such a setup, a whole new world of IGMP and multicast. I got it working, but..

The problem:
It can run for hours without problem, then starts to stutter.. They can then switch to another channel and it works fine. They can also wait about 30min to 1 hour, and it will return to normal.
All other internet traffic also runs fine while it stutters, CPU utilization not that high, etc. Everything else seems ok.
It runs fine as soon as I switch to the ISP provided router.
Also, it returns to normal when i restart the IGMP proxy service.

The setup:
In this order... Fiber box/modem, ---> Pfsense box ---> Switch ---> Smart TV box...
On the same switch is one desktop and the original ISP router to provide WiFi for their tablets and phones.
The Pfsense box is a "HP t610 PLUS" with a dual port Intel NIC.

Settings:
Pretty basic stuff, a WAN, LAN, (both on intel card), and "opt" onboard for a different isolated work related network.
I got PfBlocker-NG, and no other packages.
There is a WAN rule for multicast IP range with "IP options" enabled, and a rule for UDP traffic on specific port, from the documentation on IGMP Proxy, these rules should be unnessary but for me it doesn't work without.
Then there is a LAN rule that allows all, and other rule which allows IGMP + "IP options"

in the IGMP proxy, I have the upstream set to two ISP networks, and the downstream my lan network.

Other observation that stumble me a bit.

On the LAN traffic graph, I can see the IPTV pull 15Mbit/s smoothly, but why is it both showing in-going, and out-going? is it the nature of multicast?.
When the multicast/IGMP figured out it's stuff?, membership?, etc. The actual data for IPTV seems to be delivered via a 10.0.0.0/8 network address from the ISP, UDP. normal?.

Ideas??
What can I do ?.
My own vague ideas are that, there is something about the connection... time out.. something... loops.. fills up.. something that just locks itself in a bad state...
Or simply the proxy itself?.
The machine isn't the newest, and can get hot, but other channels and traffic works just fine.
Why does it solve itself after a while?.