3 Players: works with Hamachi - only one connects with real IP?

[Wolfo]

I was playing MHP3rd HD with a couple of friends and wanted to test Ad-Hoc without Hamachi since I hate depending on too many programs and it surprisingly worked with one of my friends. Then my other friend tries to connect and none of us can see him in the lobby yet the server DOES say he connected.

I must say though that I already had a few problems getting everyone in the lobby before. I had to leave and join multiple times, few tries ended up having to restart the server, I did manage to get everyone on at last though.

Still with a real IP it worked instantly with friend A, unlike friend B.

What could possibly cause this?
*both friends and me had PPSSPP added to Firewall Exceptions
*only me and friend A had 27312 port opened
*always worked with Hamachi (with everyone)