Legendary achievement issues

So I’ve been bored this last week and decided to tackle Halo 4 on Legendary and doing so was an absolute blast. Until that is I finished the game to not get any of the tasty achievements for doing so. Upon further review I found out it says I only completed Inifinity on Heroic (the difficulty i originally played when it released). So thinking it was some kind of fluke I set it to Legendary and play through it again. To no avail, I make it all the way through to Reclaimer and nada, still says I’ve only completed it on Heroic. What gives?

Were you connected to Xbox Live?