Do you mean the game crashes? (completely exits unexpectedly with\without an error message)
Or do you just get disconnected? (JJ2 does not exit; only the game ends with a "Connection timed out" message)

If the latter is the case, opening\forwarding the correct ports is the only solution. If you have done that, there is still something blocking the connection. We can't really help you further here, because it is a specific problem with your network configuration.

But if forwarding\opening works for other games, just not JJ2, you may have done something different or your router does not forward UDP correctly. Do the other games you use use UDP? (and thus require UDP forwarding)

(Note: You do not need to forward 10054 TCP because it is used for an outgoing connection only (to the list server). Port 10054 UDP is not used by JJ2, and does not need to be forwarded and port 10052 TCP only needs to be forwarded if you want to host games. However, these ports still may need to be opened in your firewall(s) to allow outgoing connections)