No clue what the duel mode problem is. If it worked before then it should still work.
The connection problem might be because you or the players have old style hilt files in their base directory. The hilts where everyone has the same hilt I mean. I think it does this in normal non JediMod gameplay too. Try turning on autodownload and see what they start downloading.
Also, I think there is a 128 model limit in the game, so all the hilt models + a bunch of player models might push you over that limit, and I have no clue what happens then. I would assume it just ignores the extra models but it might also cause memory errors or something.