A mark in time
 

Stop the video at the 4 second mark on the face on video. Do it a few times because there is a lot of info at different points of that 4 second mark. First I would look at your footwork, particularly the right foot. There is a good drill in Video 2 of AG that will help you become more aware of proper right foot action. Next I would look at your pivot and ask you if you feel that the pivot is really being used in the proper sequence. Lastly, I see some over acceration and the need to work on better rhythm post impact. Just my 4 seconds worth! Enjoy the journey

Hip joint flexibility
 

Some of us have reduced hip socket flexibility. This seems to be a problem for me especially on the left side. If the pivot through is restricted, the body stops,the hands flip, and for me, the ball hooks. For now, I'm turning my left foot more towards the target at address, and my shots have started to straighten out.

Anybody know an exercise to improve hip joint mobility?

You might want to look at the TPI site. http://www.mytpi.com/

They will show you how to test your hip flexibility and will also show you a variety of exercises. All at the right price.....free.