I had once ipv6 related problems (under Windows XP though).
I recently saw that Adoxa offers a tool that patches the Freelancer. exe so that ipv6 adresses are prevented
in the server list (whatever that might exactly mean and whatever the consequences of those would be.
Maybe such servers wouldn't show at all, because Freelancer is quite the dinosaur in that behalf. And since
you have problems with the server showing up I just thought ...): http://adoxa.altervista.org/freelancer/tools.html
Unfortunately there is no documentation which seems to be not uncommon with software that is offered by Adoxa.
Maybe one of the mod developers could tell if the Discovery Freelancer.exe is already patched this way.
I suggest you don't try that on your own because there's a high risk that the Anti-Cheat running on the server
might find such changes not very funny. And that might not even be the worst case scenario.