If you didn't get any join points, check after the game to see if they exist at all. Run through the game with archmages and bubble mages. If there are no join points, it's a bug; replay the game. If suspicion arises during the game, have the 3rd player check the save. I remind you that before starting the game, you need to disable the "HotA rules" checkbox (or better yet, disable HotA altogether). If the game is played on a mirror (i.e., without HotA, it won't work), update the HD mod; Baratortch said he fixed the bug. And just in case, don't use the automatic restart.