Mission Progress not registering as completed

I’m trying to playthrough Halo Reach MCC on PC on Heroic, I get through the Pillar of Autumn, sit through the Epilogue and do the Lone Wolf mission. I then get back to the Main Menu, for it to tell me that I haven’t completed the Pillar of Autumn mission at all, however Epilogue and Lone Wolf are completed. So my mission progress is at 11/12.

I wait 24 hours and see its not changed so I try it again, doing the exact same thing but skipping the cutscenes. Finish the mission on Heroic again and still nothing. This is incredibly frustrating as I am 1 mission away from completing the game and I have completed it twice now. Both times taking at least half an hour.

Is anyone else having this problem? Does anybody have a fix?

In your profile say than that mission is missing. Maybe you lost the internet conection at the end or something like that