I dont know if this is a bug, a oversight or just a direct nerf hidden as a buff. But in the recent patch riot changed the way Fiora's Riposte(w) works the intention was to make it able to use Kennen and Braums passives to stun instead of just delay their stuns (which is how its supposed to work), but with that change came a nightmare. A lot and i mean a lot of abilities also got effected by this so some "side effects" would also go through her w.
Some Examples are:
Quinn's Blinding Assault (q) still blinds
Lee sin's Sonic wave (q) still makes him able to jump
Vlad's Hemoplague(r) goes right through it when cast
Zed's Death mark(r) goes right through it when cast
Tbh this has left fiora really weak as what she could do earlier to outplay has been completly removen and makes her much more woundable to a lot of abilities which i dont think was the intention when they clearly stated it as a buff.