Legendary In Under 3 Hours Achievement Bug

A few weeks ago, me and a friend completed Halo 3 on Legendary in 2:54:58. He got the achievement for completing Halo 3 in under three hours. I did not. Just this morning, we finished ODST. He got the “Nagato Makes Moving Easy” Achievement, and I didn’t. Is this a common issue?

> 2535431338164751;1:
> A few weeks ago, me and a friend completed Halo 3 on Legendary in 2:54:58. He got the achievement for completing Halo 3 in under three hours. I did not. Just this morning, we finished ODST. He got the “Nagato Makes Moving Easy” Achievement, and I didn’t. Is this a common issue?

The achievement for Halo 3 Legendary under 3 hours didn’t trigger for me right away as well (a mixture of solo and co-op times). After replaying “Arrival” and “Prologue”, and then restarting the game, it triggered correctly. See if doing any of that solves it.

> 2535437634126668;2:
> > 2535431338164751;1:
> > A few weeks ago, me and a friend completed Halo 3 on Legendary in 2:54:58. He got the achievement for completing Halo 3 in under three hours. I did not. Just this morning, we finished ODST. He got the “Nagato Makes Moving Easy” Achievement, and I didn’t. Is this a common issue?
>
> The achievement for Halo 3 Legendary under 3 hours didn’t trigger for me right away as well (a mixture of solo and co-op times). After replaying “Arrival” and “Prologue”, and then restarting the game, it triggered correctly. See if doing any of that solves it.

Didn’t seem to work for me. Thanks for trying to help.

> 2535431338164751;1:
> A few weeks ago, me and a friend completed Halo 3 on Legendary in 2:54:58. He got the achievement for completing Halo 3 in under three hours. I did not. Just this morning, we finished ODST. He got the “Nagato Makes Moving Easy” Achievement, and I didn’t. Is this a common issue?

So frustrating how buggy all of the achievements are. Such a waste of time if you’re actually trying to go after one. And no one in the game or MOTDs is it stated that like 10% or more of the achievements are bugged in some way.