well 343, whats up, ive done them all on heroic 
No idea what you are talking about, I got it just as the text āEpisode completeā was shown (I did mine on solo legendary) But it says any difficullty in the achivement! Go back and look if you missed out on a map or two!
I donāt have it either. But I have each episode completed, confirmed it in the selection.
I do have 1-3 on legendary and 4-5 on heroic not sure if that matters. Also variations of matchmaking/non match-made, wonder if that matters.
Its bugged, play any mission solo and it will unlock.
100% sure they messed up this achievement.
Iām sure you had to do each episode in the āfind a matchā option. As in MM heroic co-op. You canāt go back and re-do any of the old weeks in MM either.
> well 343, whats up, ive done them all on heroic
just go play a game of spartan ops solo, any level any difficulty and it will unlock.