I have just completed halo reach under 3 hours on legendary with two friends and I am the only person not to receive the achievement. Very frustrating when I am the only person out the group who wanted said achievement. I can look at the leaderboards and all the campaign timings are there and the same as my friends who received the achievement. Anyone know how or where I could get this resolved?
Loading up a campaign mission and running through it again usually does the trick.