No Chest after getting S

So, ive been playing alone alot lately which made me play mains mostly and thereby havent gotten a chest in weeks, no problem. i decide to try get one and after i get S and with 4 avaliable chests then nothing, no chest... i tohught it was a 100% chance after getting S? i even got an S+ on evelynn yesterday and still no chests rewarded. it clearly state that after getting S- from playing alone will reward you a chest, no if or but's( in the launcher under profile ).