Just a mention on the issue of this achivement not popping:
DO NOT TRUST THE GOLD MEDALS ON CHAPTER SELECT.
I had all 4 chapters with a gold medal, and no cheevo. I was rebooting and restarting and clearing xbox cache... waited 3 days.... nothing worked.
The item written in comments by SuperArtTeacher ended up solving it for me:SuperArtTeacher said:
Same issue happened to me. I quit game, went back in and all the chapters had the medals, but when I looked at each section in a chapter I noticed one was graded out again. Went back in and got it again and achievement popped. It now shows 23/22 for chapter 4 for me. Hope this helps
After doing this, my collectible shows 23/22 and.... wait for it... the GOLD MEDAL on that chapter is now gone (but achievement popped immediately).