So, I know that there are issues with the campaign achievements, but I wanted to report mine in detail just in case these issues have not been explicitly reported already.
I am reporting 2 issues. I am playing campaign local-co-op with my wife (who has a different XBOX Live gamertag than me).
1) Campaign “mission” does not appear as completed unless I beat the entire level from start to finish in one run. If we beat the “ALPHA” section of the level, quit the level, return and start playing from the “BRAVO” section, and subsequently beat the rest of the level my wife and I both receive an achievement for beating the level, but the mission does not appear as completed in the campaign-missions screen (it shows that the level has not been completed on single, or co-op play, whilst other levels that were completed in one run, show the heroic icon and a level score for the completed level).
Summary: I think this should be somewhat easy to address since the game awards us the achievement for completing the level, just not the indicator in the campaign lobby.
2) Related to the first question: although my wife’s gamertag gets the achievement for completing the level, relatively few (only 3 or 4) of the missions appear as completed in the campaign lobby. When we play co-op, her gamertag is not the session leader (mine is), so I am assuming that has something to do with it.