I have played several games on Daybreak, Outcast, and Perdition from start to finish. It’s the second to last achievement I need to unlock in this game and it won’t unlock. It’s also very frustrating because Perdition and Outcast never come up because people don’t have the maps. Why do I buy maps that I can’t play? I have tried deleting the DLC and reinstalling it but it doesn’t help. Very Frustrating.
You may wish to post in this thread about Halo 4 achievement issues. As seen in this post, you are at least the 2nd person having this issue. I have also read a post by dresdenWII on TrueAchievements.com; he is also unable to unlock Sight Seeing.
It seems like more than a coincidence that suddenly, and near simultaneously, 3 people are having trouble.