If you feel it is rhythm, go and practice 50-meter pitch shots, ensuring that you maintain the same speed up, down and through the ball. Another favorite exercise of mine is to hum throughout your swing if the pitch or tone of your humming changes you are “forcing” the swing.
Finally, the one I expect most will choose is balance. If you fall backward away from the target, the ball or you fall forward towards the ball or the target you have a very big issue that needs to be addressed immediately.
So how can you work on balance? The best drill which will help ALL balance issues is to stand with your feet and knees together (if you can physically do that) and hit half shots
with a 7 iron. With your feet together you will be aware of exactly how your body works to maintain balance. You will probably be surprised at how cleanly you strike the ball and how easy it is to get the ball traveling through the air, as far if not further than normal.
When you do this drill be sure not to get obsessed with doing it, you also need to hit balls in a normal fashion.