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When I get close to the top of my backswing my thumb pad part of my left hand begins to seperate from my right hand when I try to keep a flat right wrist. My grip is neutral to slightly strong I believe. I am curious if there is something obvious I could be doing wrong to cause this and what kind of issues this could be causing in my swing (my swing is very inconsistent).
I get the same thing, but in my case it is becuse of an old hand injury which did not heal correctly and doesn't allow me to fully cock back my right wrist (your left), which prevents me from having the correct angle at the top with my right forearm...
I have learned to overcome it by having a strong right hand grip...
One thing I have found is that the flat left (right

) wrist position at the top is easier to achieve with a neutral left hand grip, combined with a slightly strong right hand grip...
You could probably achieve the same with both hands neutral...
maybe you left hand has crept up on top of the grip a little at address,and if you have a strong right hand grip you will find it harder to get the flat right hand at the top...