Premium Hextech Chest not giving skin of an owned champion

I was told by a friend, and multiple online sources, have indicated that one of the premium chests will give you a skin for an owned champion. The first chest worked fine giving me the usual Ashe and Garen shards, though the second one gave the usual (I think) Sanguine Garen skin and a ward skin, it also gave me a skin for Nautilus, not Vel'Koz (The first and only champion I bought/owned, which I got recently). I don't know if there's some change to the chests I'm unaware of, or if it takes a while for the game to recognize that I actually own my champion, or maybe I have to play a game with them. Maybe it's just a straight up glitch. Either way it's severely disappointing, because I plan on maining Vel'Koz, and I can never get a chest guaranteed to give me a skin of a champion I own ever again. Obviously some way to "fix" this is extremely unlikely, just looking for an explanation.