I too was a “1 Day Rider” on Saturday and still have some numbness that concerns me. Although mine is in an area that is far greater importance to me.
I have also delt with hand and feet numbness in the past and in my experience the issue was normally further up the arm and or shoulder than you’d think. I can move around on my bars all I want but the feeling doesn’t come back until I actually sit up and ride with no hands. The feeling usually comes back almost instantly. It could be that a muscle that is slightly inflamed could be stressing or compressing a nerve. The problem could be all the way up in your shoulders and neck even. Holding your head up for 10 hours is a lot work for those muscles, especially in the aero position. Hope this helps and keep me posted.