mandatory quest breaking in the post-game

im trying to do the post-game quest with Sadie where you help her steal back a hostage from some guys in a canyon

but every time i get to a specific part where you get off the horses and look into the canyon, everything just stops. she crouches behind a boulder and says nothing, and the guys in the canyon put the hostage down, and then nothing.

i even tried going down into the canyon, and the guys didnt even react to my presence, or when i killed them

i tried killing myself, that just crashed the game, and no matter how far away i go, the quest doesnt fail, so i cant just load a checkpoint