S Rank in normal game but no chest.

Image of collection screen with no chest on Karthus

I've been going through my champions in normal games to earn chests and finally played a decent game on karthus. I scored S rank as shown by my collection screen and match history screen. As the collection screen shows, I have not earned a chest with karthus this season. Not sure why a chest was not rewarded.

Edit: Does the collection screen not show that I've recieved a chest for a champion if one of my premades earns the chest? That would really make hunting chests confusing.