Here are two things I have noticed:
Thats all I have noticed so far, but I'll keep an eye out. Also RIP my chest from my S 
game ;-;
Fondling Gems1 votesfor 1, try checking your shard menu, mine showed up there, and you only get chests for YOUR S ranks
Zombiemaster1 votesActually, you are able to get a chest when someone else on your team gets an S rank, but you do have to be in a premade party with them.
HaruTheDoggo1 votesI did get an S, I got an S on anivia and it said "You have received a key fragment!" and i didn't get a chest. I just got another s with her and got the chest anyways.
Fondling Gems1 votesYeah def a bug then, a lot of them are floating around right now. At least there was no lasting harm and I am sure Rito is working to clear up the bugs as quickly as they can.
Zombiemaster1 votesFor 2, that is intended. You are only able to get one chest per champion, and getting 2 chests in the same game would be like getting 2 chests for one champion.
Wiz100111 votesFor 2, that is intended. You are only able to get one chest per champion, and getting 2 chests in the same game would be like getting 2 chests for one champion.
actualy, if your teammate gets an S- it counts the chest for THAT champion, not yours.
Zombiemaster1 votesIf you go here and click the "Hextech Chest" option, there will be 4 bullet points, with the 3rd one stating this:
If someone in your premade group earns an S rank, you’ll receive a chest as well! The chest you receive is tied to the champion you’re playing, so that champion will be unable to earn more chests for this season.
It doesn't matter if your teammate is the one the got the S rank, the chest you get is for the one you played, not theirs.
HaruTheDoggo1 votesI miss read that part when I was glancing at the update post. I thought is was anyone on your team, not just premades. Thanks for bring that to my attention.