Yeah, pretty much the same problem here.
Tried everything with router/firewall/ports, but problem is only with Arma3.
Quite "frustrating" not being able to play with friends.
No problem at all joining other servos, just cant host any game.
Hope BI will solve this problem SOON.

Hello !
No, with the latest Dev. build, so far this problem did not reproduce.
So far so good !
Good job !