Monsters unable to perform tactical summons in current version of the game. Maybe computer players too but I haven't seen that in action yet. This is funny because this is something that has worked fine in earlier versions of the game for as long as I have played it. My own heroes can perform tactical summons and it works properly. But if a monster performs a tactical summons, the game doesn't lock or crash or anything, the spell appears to complete correctly but no additional enemy appears. This happens every time, no exceptions.