
just my opinion once again, but when you try to break boards, it seems ( seen from my lack of experience of course) your shoulder does not really follow your hips.
Watch closely your friend : his whole body is moving, and watch closely yours, it seems like you move different parts of your body at different moment. at 0:31, 0:32 stop the video and you will see your arm in front of you, but your hips still on the same place.
For your friend, the shoulder follows more clearly the hips.
In pushhands, compare again your body position and your friend's : it seems you do not really try to keep the body upright, at 2:07 your shoulders are working, but not your hips.
at 1:11 when you come back to your friend, you put yourself out of balance, once again because you do not keep your body aligned.
To keep the body aligned anywhere, anytime, could be the first point to train for you.