I have a 12 year old....I'm no expert and I'm not a coach...but my kid can hit and I have listened to hundreds of batting practices. My comments are:
1. Why is his back foot coming off the ground at all? If you look closely he is not pivoting his back foot he is actually lifting it up, moving it, then pivoting. He took away his base of power which throws him off balance. Try going back to the basics of squishing that bug.
2. He looks too tall in his stance, he's actually coming down to hit the ball at which point his weight isn't shifting from his back leg to his front leg because he's barely got any weight on his back leg. He should start a bit lower, weight on back leg, then transition the weight from the back leg to the front, this will bring his hips around more naturally because right now he is getting his hips around but it's out of memory not mechanics and I'm not seeing an actual balance transfer.
Those two main things can throw off his balance and if you don't have balance while hitting it's not going to work....biggest problem in my opinion is lifting up that back foot at all...he seems so focused on turning his hips that he isn't remembering to pivot.