I've already hosted games for some friends and played on public games with other players with no problems. But there's a specific friend of mine that can't play on any host. He gets disconnected after a few seconds and is presented with a modal telling him that the connection was lost because of a unknown reason.
By the way, we're playong online, already enabled UPnP and fowarded the UDP port.
Any suggestion for a way to debug the connection error?