Crazy Hextech Chest Bug in Premade

So me and my friend like to play together quite a lot, he was playing new champs and he ended up getting an s- on yasuo while I was playing skarner and I got an a-, and at the end for whatever reason he didn't get a chest, but I got one for "d rank" but again, I only scored a- and it says "chest acquired" on skarner, this also happened to the same friend my last game with nunu jg "me" and caitlyn mid "friend" and i "Stole" his chest... Might want to be looked into... Idk if this is common... also, he said he didn't the chests so I quite literally "stole" them.