Yes, I think it could be classified as game-breaker. I'm getting the same issue, and I know of at least one other case. It's especially infuriating because I'm really enjoying the game, finding it to be one of my favourites of the year, and then it's stuck. Now I'm doing side-missions and waiting on a patch.
Apparently at least half of it's explainable, though. I heard somewhere else that the arms dealer dissapears after you've done three or so missions with him and only reappears following your move to the second district. So that part isn't broken, exactly, but it's stuck until you can complete more missions, so it's not going anywhere as far as we're concerned.