Fiora Vital proc bug

Any reason as to why Fiora does not proc the Vital on an enemy if she's attacking him from too close? Multiple games there were times when I found myself sitting literally on top of the vital and it not proc'ing on auto-attack. Also times when I Q'd past an opponent just barely making it to the other side, and the damage would go on the Vital direction but it would still not proc.

This makes Fiora's core gameplay insanely unreliable and I would rly appreciate if Riot looked into it.