Mission 17 glitch#883

in Mission 17 of the main campaign missions, the game outright freezes completely when the boss is near death.

yeah when the boss near death and sometime when the boss appear it freeze the game.

the game keeps crashing at this mission at around the same point the moment the boss gets below 50% health i tried every thing from running the game in administrator to different graphic level, restarting my pc or the steam multiple times, doing other missions first or joining multiplayer it has no other result than crashing what should i do now?