Arrows bounce off mobs

I have an enchanted bow in a survival game where it has Power V and punch I which works for the most part. Randomly it seems as though the bow will misfire, and arrows will occasionally bounce off mobs and hit the ground, dealing no damage to the mob at all. This bug is infrequent and occurs randomly. I always charge the bow to full drawback or nearly full drawback when this happens.

No, the mob is not on fire or taking damage prior to the arrow's impact.