Board Thread:Questions and Answers/@comment-30771283-20171113094245/@comment-1327106-20171127023744

I don't have the game right in front of me anymore (my brother has had it on loan for a few months now), but I don't think that Survey Missions count towards Attack Mode except when it comes to the epilogue missions. If you've finished all the epilogue missions, you should have 100% of Attack Mode down and unlocked the "Humanity will feast upon the Titans!" trophy/achievement depending on which platform you're on.

If you did that and still don't have 100%, I would guess that you need to do something like S-rank them all, but to be honest, I don't even remember that Attack Mode had a completion percentage at all so I could be way off. If I hit 100% myself it was probably because it happened along the way to another trophy.