Grasp of the Undying proc failing to trigger

When playing a ranged champion, Grasp of the Undying will fail to proc if you move outside of your basic attack range before your projectile hits the enemy champion. The damage from your attack still occurs but the hp buff, heal (if you have missing HP), and animation fail to activate.

I just played a Karma top game where the buff would fail to proc on about a third of my attacks.