Haven't been getting chests for S grades for no apparent reason

I noticed these past 2 weeks or so I haven't been receiving any chests or key fragments for wins with S grades from me or my arranged teammates. On my profile it says I have 4 chests available to receive, and when I look at my champion collection NONE of them have the border that signifies you have gotten a chest for them this season. Can someone please explain why this is happening because it's pretty crappy to not receive the rewards I should be getting for doing well.