i was playing a ranked game as aatrox and got killed due to the item not working as intended, its hard enough chasing champs down as aatrox let alone getting away when i cant move through minions after buying a PD.
witnessed this, really sad game changing moment.
You need to be within 550 units of a visible enemy champion in order to ignore unit collision, and it doesn't look like you were within 550 units of Vayne while you were being creep blocked. For reference, Vaynes AA range is 550, so if she can't auto attack you, then you won't ignore unit collision.
EDIT: After some searching, you actually need to be within 500 units of a visible enemy champion to ignore unit collision, as per patch 5.22, and it hasn't been raised to 550 at all since. This is a bug with tooltip giving the incorrect unit amount.
This means that if Vayne is auto attacking at her max range, you still wouldn't be able to ignore unit collision.
It's cost a 550 range on it. Like all game objects it has a check statement. You can see that the you were caught stuttering moments before vayne got in range for the auto attack (which happens to be 550). You flashed right as her attack animation started which would have also been the moment you gain PD passive. It was just a very unfortunate timing/moment for you. But had you kept walking if no flash was up it would have most likely triggered the passive.
