Cho'Gath Feral Scream deals no damage to minions bug

I observed a bug where my feral scream dealt no damage to minions at least twice in the same game.

I'm unclear on what conditions caused this. Another player in the same game noticed the bug as well, so it wasn't just a visual bug on my client affecting the minions location.

On at least one of these occasions there were no other abilities/statuses affecting me or the minions.