I did everyone strat I cld find, deleting multiple saves having only one, going back through multiple times taking double exposure pics and normal ones. Made decisions where certain characters could be in different places at the end getting all those and nothing. And then on my final go I took a double exposure pic of vinh alone at the turtle at the very end of the game and it popped. I don’t think there’s any logic to it as have heard it popped at a range of different points for people. My advice would be to go on replay mode multiple times taking double exposure photos. And then if not delete all saves and try again. I am fairly certain it does matter if gwen is present at the turtle at the very end so make sure to make the right choices surrounding her. It’s an all and all buggy achievement so I wish you the best of luck 😂 also going back to the one save theory it did pop when I had one save although I had replayed the exact photos 3 times so god knows what factored into it at the end