Not receiving chests from getting an S- or better

Currently I am trying to level up my Kha'Zix Masteries but i am 50 blue essence short, so i've been playing a few games to try and get a chest so i can get some more blue essence hopefully, but in the past few games I've played and someone got an S- or better, they didn't get a chest? Did Riot remove this from the game or is it in only certain games? I don't know