Legend achievement

So I recently got to the level that legendary dragons spawn in skyrim I've killed three or four different ones I've killed multiple other dragons after the fact and the achievement still doesn't pop for me. It's getting annoying as it's one of the last two achievements I need to get all of them I hate that for some reason the gane is deciding that it doesn't count I've tried everything I can think of to make it work. I'd like this resolved. And while on the topic of achievements for some reason the achievement system is delayed like I can do something required for an achievement and it'll pop up and hour later.

:)