About 1 year ago I was in contact with a technician from init7 because of another problem.
According to him, MultiCast does not work with Crossover7.
It only works with Fiber 7 if you are directly connected to their own network.
With Crossover7 you are still using the network infrastructure of another supplier.
That's why you also have the Vlan11 and the PPPoE login which you have to set in the router.
On this VLan11 you get to the init7 network and log in there, with the PPPoE login data, to their entry points.

I can confirm the problem. I recently put a 5590 with Crossover7 into operation and multicast does not work.
Has anyone been able to solve the problem?
Init7 support does not know the problem or the solution.
I would like to ask AVM about this soon.

Here are the instructions for the FritzBox 5490 ... the 5590 is a successor model:
https://www.init7.net/de...

I don't know if the box can handle the multicast signal on TV7, but I'm at https://www.iway.ch/ and I don't really see any problem...
https://ch.avm.de/service...
https://avm.de/service...