People with injuries to or impingement on the nerves as they proceed from the spine will sometimes have symptoms in the hands with no symptoms between the impingement site and the hand symptom.
For example, a person might have numb or tingling thumbs, thumb and index finger, fingers, and etc., without any symptoms in the neck, shoulder, upper arm or lower arm.
Nonetheless, the symptoms have their root cause in the neck and not in the hands.
My point?
Play with position on the bike with a mind to how it effects the neck.
Yes, the symptoms could come from too much weight on the hands.