I read about a game breaking glitch on Gamefaqs, and the exact thing that happened to that poster happened to me but my game was fine. It appears to be random. Anyway, your objective on this particular mission is not to kill the zombies, you're actually supposed to run away and go back to the safehouse. I wonder if she's tried just following these steps and then returning to the safehouse? If not, that sucks. Hopefully Ubisoft patches this.
Also, she says this is about an hour in. Not sure about that, this is literally the first mission you go on, the supermarket is the first building you get to besides the safe house.
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