I have seen run after run where the three grunts just outside of the bridge don't exist, PC, OG Xbox, MCC, yet when I boot up the game through MCC I always encounter them. Even when I switched from walking backwards to get ammo to following what everybody else does.

Is there a different version everybody runs on? Or enemy spawn manipulation I'm not seeing. This game doesn't have many guides (that I can find), especially for this sort of thing.

The three grunts only spawn in if you leave the bridge area too slowly, if you leave before you get a checkpoint they do not spawn in.