When you swing the club back and consequently up, you might have a tendency to rise up with it. That is, raise your body up a bit.
That gives your swing a new bottoming out point, and you have to go reaching for the ball as you go through impact. This is so easy to do without being aware of it.
Give this a try. Swing back and tell yourself to keep your head where it is. Don’t let it rise up.
If you do that, and it feels odd, then you have habit of rising up in the swing that needs to be broken.
How do you break the habit? Practice swinging without your head rising up.
Good point, Bob. It relates to some advice Arron Olberholser gave: “Maintain your levels.”
If we keep a “steady heady,” we’re less likely to go up and/or down. Remaining “on the level” will typically result in better ball striking.