The hold button is incredibly finicky. It has two ways to go wrong.
+ First, beware, a new command you issue that causes them to move will override the Hold command. I assume you're playing in tac cam if you're manually positioning team mates? Because in regular mode, AI-controlled companions do more things themselves, so I really have no idea if Hold button is even feasible there. Anyway, things that will override the Hold command even in tac cam:
-entering or finishing combat. As in, every time they reach for their weapons or put them away. So if you're closing rifts, be ready to re-apply Hold before the second wave or everyone will run towards your lead character!
-telling the character to move to somewhere. If they're ranged and content to attack, they might stay there. But they're not on hold anymore. Re-apply the hold button if you move your lead character further away or they might follow!
+ Second, beware, they will completely ignore their Hold command if a ranged character has no line of sight to their target. They will try to resolve this by running forward until they do have line of sight. Ending with the lovely sight or your archers trying to hug the enemies.
Good way to get them to stay put: Enter fight, immediately click Hold. Then move everyone into position. Take care that the ranged characters have line of sight. That usually does the trick and I hardly ever now have problems with melee-happy archers or mages.
That said, it's incredibly tedious. I loathe the new hold button. If I put them somewhere I want them to stay put, damn it. grrr