I agree that this seems to be a multiplayer bug of some kind involving desync or tickrate. I typically fly with a human CPG and it is nigh impossible to hit a moving target in multiplayer with Hellfires unless shooting from directly head on or tail on, but even then odds are less than 50/50 of a direct hit. When this happens, the missile always hits behind the moving target.
In my experience, it seems like the missile tracks directly to where the TADS was looking when the missile was fired rather than tracking the moving target. I have even seen 2 missiles hit in the same spot behind a moving target when the target was being tracked by IAT.
Of note, we haven't tried LOAL to see if that changes the behavior, but we'll give a whirl and report back.