Halo 3 ODST co-op LASO broken achievement

I just finished the LASO playlist on Halo 3 ODST tonight and I did it in a co-op game with one of my friends. For the last week, we had been playing through it and we played every mission together and my friend was the host every night. In the end, he got the achievement and I got a playlist that says I still need to watch the epilogue but every time I try to finish the last part of the playlist, it puts me into the first mission and I have to restart. Not only am I mad that I will have to restart the LASO playlist to get the achievement when I already completed it, but even their Classic achievement that I have done five times is still “Done, Unlocking…”. I understand that this is a free add on for being an early adopter of the game but this is ridiculous. For being a halo fan from the beginning, I have lost faith in the new developer that is sending the series down the drain. I am disappointed with 343i putting half effort with their one gaming franchise that they are responsible for. Anyone else having these achievement problems?

Yeah I had to beat odst 3 times before I got the laso achievement. the first two times I wasn’t host but then I was for the third time and I finally got it.

You have to be host on coastal highway in order for it to guarantee to pop.