Graves' auto interactions towards Yorik spirits

I played a game of Graves versus Yorik in the top lane and noticed that my autos do not always hit Yorik spirits. Sometimes, even when they are the only enemy targets in the vicinity, Graves' autos do not hit Yoriks spirits, resulting in a damageless auto attack on the spirit. However, the autos never missed twice in a row, so the shot following the one that did no damage does damage. I apologize as I have no footage or screenshots of the interaction.