Since the other posts are kind of old, if you need to unlock this achievement but have no one in your friendlist with it, send me a request and I'll add you. I just recently unlocked this achievement and I know how frustrating this can be (especially if you're trying to 100% the game)....

good game

---------- Edit: WE FOUND THE PROBLEM! The game won't load the leaderboard if you have over 100 friends! Just go to your friends page, select "Manage Friends", select all, and uncheck a friend who has played the game. Then Block everyone else. It's not

So I've done some research on this mode after finishing the story. I'm considering it, not really sure i want to put myself through it. To my understanding there are just 2 checkpoints, the end of parts 1 and 2. However if I get to one of these points then shut down the game to come back later, will i start from the beginning of the entire game again? If so, this is literally hell......