I always got a red random guard walking around, but a different place each new game. Twice around the drow though, once by the hobgoblin interrogating the corpse. Not a scripted anything and no chance for checks.That's why I said bug not ambush and why I am asking unstead of just trying again.
So if you walk past everything, it ends the same, or you can side with them against the grove? like different content. Or just sneak/bluff through them and take the boat skipping content?