I don't know exactly why it doesn't work, but I found the answer.
Try to delete all the friends lists
That way it works as normal as a lie.
It's not a NAT type problem, and it's not a wired or wireless problem.
What's clear is that Ubisoft doesn't intend to solve this problem.
I've tried everything I could,
This is the clearest way to solve the problem.
Try it as I say and it'll definitely work.