At the end of Kiizingo Boulevard on Halo 3: ODST where your fighting off the two waves of covenant, after I finished the last wave of covenant, on Heroic Difficulty, I was not able to get the last trigger from Dutch says: “Way to Go, Mickey! Come to my position”. They don’t say anything and I doubled tripled check the area for anymore covenant and there were none. Tried reloading the checkpoint to part of the last wave and that didn’t make any difference after I saw all covenant dead. Dutch just stood there with no trigger to end the mission.
I then tried restarting the mission again, played through it up to the last wave again and that bug was still there! I then tried to reload the last checkpoint about two more times, then the trigger finally happened and I could end the mission! I had no trouble with the Dutch trigger on Easy, Normal, and Legendary difficulties but on Heroic this started to happen.
Sorta happened to me yesterday. I walked around and was positive that all the enemies were dead, but turns out that a jackal somehow fell through a crack between one of the outer walls and a staircase. Kinda funny because the crack was too small for me to fall through so I threw a grenade and managed to kill it. I’m sure this is pretty rare but it may have been the case.
I also had another game breaking trigger bug on Kilowani Station as well today on the same difficulty! After you kill the Phantom in the transition tunnel area the 2nd time with one of the big covenant exploding structures on the ground below it, the game does not trigger the next door meaning I cannot proceed any further! Tried reloading the checkpoint, but it put me after I killed everything in the tunnel with the door not opening. Restarted the level, then it worked this time. Did not have this issue on Easy, Normal or Legendary difficulties.
I think there was also a bugged trigger on Data Hive after you rescue Virgil where Buck and Dare have a dialogue about the Engineer to open the first door with the Engineer, the Engineer was stuck in the previous room with the Drones on the Ceiling.