Hey there, there is a bug where playing 'The Invitation' on Legendary will also mark 'Commencement' off on the Legendary triumph. That can cause players to skip a Legendary Commencement run, thinking it was done or not needed. That's what I think happened here. Above and beyond redeeming the triumph, to qualify a character for their class exotic campaign reward, they need to have played all 14 missions on Legendary - so despite the above, it is still necessary to play Commencement on Legendary on that character. Play that on your Hunter, then check the Altar of Relativity on Kepler. Once the triumph is completed, the exotics can drop from 'The Sieve' post-campaign activity, regardless of whether any class individually did all 14 missions (so in cases where the Legendary missions are split across characters), but you may as well claim the Hunter's freebie since there's only one mission left for that.