Fiora W not Stunning on-hit stuns with her w

I was playing a game as fiora on patch 7.4 when I outplayed a TF using my Reposte. A few days later I was playing against my friend in the same matchup TF vs. Fiora, but when I reposted his w and hit him with my w nobody was stunned. I thought that was weird so we tried it over and over and it continued to not work properly. Later I learned that it wasnt only TF but all on-hit cc like renekton w, blitzcrank e, leona q, etc. I would like to have this fixed because it is especially annoying toplane in the renekton vs. fiora matchup, even if I outplay him and properly predict when he is stunning he neither of us will get stunned :(