I'm unsure what VFX is, but I would expect that when the character ripostes he would swing the weapon, as that's what a riposte is. Obviously when I cast vengeance the sword swing animation fires, but when the enemy hits me back and I riposte, there is no swing.
VFX is Visual Effects. The FX kinda sounds like effects so it's not really an initialism.
That is working as intended. You'll see a small VFX of a sword hitting the enemy when it happens. We can't have the character animate because riposte will most of the time trigger while you are in the middle of another action that requires you to be animating doing something else.