I thought we were supposed to get a chest if someone from our pre-made party attained S-, S, or S+ rank. Just played a Normal game where a player from my pre-made party earned S+ on Ahri, and the other 2 players (who didn't own Ahri) from the same pre-made party, earned a hextech chest whilst I didn't. This has happened a few times now :// I've also gotten S-class on champions myself without gaining any chests afterwards.
You can only earn one chest per champion per season. If you are playing a champion with whom you have already earned a chest, then you cannot earn another chest on that champion until next season, even if you get you S rank with them.
Also, when a premade friend gets an S rank to get you a chest, the chest you get is counted for the champion that you are playing, not the champion your friend is playing. So, if you are playing a champion with whom you have already earned a chest and someone in your premade party gets an S rank for that game, then you will not earn a chest.
Do any of the reasons stated in this article apply to you? https://support.riotgames.com/hc/en-us/articles/207884233-Hextech-Crafting-Guide
