"The War to End All Wars" achievement did not open.

I also have this problem. I assume the achievement flag is set once on your save and never procs again. I completed the campaign on Hard when ea play had a free month or something, and then when I bought the game on Steam I still had my save and I didn't get the achievements. I believe I can just erase my single player save and do it again without effecting my multiplayer profile, but I can't be bothered yet after doing it more than twice.