Problems I can't solve with the Volley support.

There's some trouble with the Volley support that I can't understand. Some mobs just won't die. If the accuracy is poor, the situation is much worse, but I don't think it directly affects it. If I give up this support gem, the problem is fixed. Could this be a skill-bug problem ?
Video:https://youtu.be/sH58QPcmGNo