Not getting stars in nightmare difficulty

I want to know about you guys who have beaten at least 1 level on nightmare story mode, because even if I get 3 stars at the end of the level when I get to to the map, those levels already beaten with 3 stars appear with 0 stars, I should also point out that I am playing on hardcore, idk if that might have something to do but it's an extra info. So I would appreciate if someone who has already beaten any nightmare level had this problem especially on hardcore.