I’ve picked up some of the achievements from the Crimson Map Pack, they show up on my XBox Live but not in Waypoint. I think that you might need to take a look at it in case I’m not the only one affected.
I’m having the same issue. ODST, Pump Yer Brakes, Clay Pigeon, Special Delivery and David and Goliath are missing for me as well on Waypoint, but my profile shows I’ve earned them.
It’s a bit more widespread than I first thought. I just noticed that if you look on your Halo 4 career overview page it lists the total number of achievements as 49 (the game) and not as it should be now at 57 (game + map pack).
On top of that Waypoint on Xbox doesn’t list the DLC achievements at all!