I'm not trying to say it's the cause, but it can explain a lot of clips posted in the thread.
What my post proves is that hit animation and sound can sometimes be played even when you don't actually hit the soul. You can't rely on sound or animation (even in replays, which are server-side) to claim that you hit it, as you've done a couple of times in this thread
Of course, the animation should only play when you actually hit it, and there's no doubt it's a bug that needs to be fixed.
However, my previous post doesn't explain some clips like this one
Where player was actually aiming directly at the soul.
View attachment 20244View attachment 20243
I don't know what happened there. My best guess is that the soul was on the very edge of the quick melee range, and because it doesn't travel directly upward, it was slightly out of range, but the animation and sound still played.