Not sure where to put this as I'm not sure if it's a bug or not. But I'm sure you've noticed that with turret shots and minion damage it can seem a little... delayed? I can't remember which game it was, or who it was between but this actually was very evident in a professional match. I can't remember the details exactly, but last year a Shen used his ultimate to save a teammate after a dive (I think it was the adc?) but it looked like the turret shot should have hit before the shield went up. The casters even commented on it. But it's the same with minion projectiles as well.
I'm not sure what it is with these projectiles but the collision time seems to be inconsistent. I'll admit, sometimes they do seem to deal the damage exactly when they hit you, but other times it can seem to take about half a second for the damage to follow through. This makes more of a difference than you think. Have you ever had it where you flash away, thinking you got away safely and then you randomly die (with having no projectiles having followed through the flash?). If that were to happen with a champion auto (I'm talking about ranged champions, not melee) it would immediately be called up on. It's nothing too major as it is basically a part of life for farming and is pretty much a part of league now. I'm just curious whether it was intended like that or whether it's just a remnant from the early days of league.