I couldn't find my save data either, but I may have the solution to how to get this now. Of course this is with the patch. As you know first and foremost you will need to unlock all levels.
All 22! Just to play it safe. Then do you notice there are 15 total chapters. Some of these chapters have two parts. the first part and usually a boss fight which is the conclusion.
Try this. Play all of these conclusions and get an A rank or above. Do them in one playthrough if ya can. If it freezes turn off Xbox and continue where it froze.
But I am pretty sure you only need to play through the 8 boss/conclusion levels. That is what the two guys on TrueAchievements said.
Now does anyone know if you can play single player first then go back and do multuplayer? Still if this is screwed up I need to get on TA and find a partner to play through this game on easy all 22 levels. Then I will just do boss fights on easy, and it will count toward completion so once all 22 levels are unlocked you will only have to play the boss levels I think. If it lets you select the difficulty. not sure though.