Didn't Get a Hextech Chest After Getting an S+ Grade.

At 11:30~11:40 PM (London Time) my brother and I were playing a match and we did quite good, My brother got a S+ with Garen and I got a S+ with Soraka. We both had chests due to drop at anytime now, but, we didn't get one. We waited in the post-match lobby but we still didn't get a Hextech chest. In my match history it shows me that i earned a S+ grade but in the Collection Tab When i saw my season highest grade for Soraka is an S grade : /. Here Is The Screenshot of Match History . Here is Another Screenshot showing that I have 2 Chests Due.