Did you use a drill with a sanding disc? The filler is much softer than the coverstock, and if you go way deep into the thumb hole it surely widens the hole/shaft. I bet you have a pitch change, even a problem, now, due to the widened hole. Tape might help getting it bacik tio s anug diameter, but I am sure the pitch feels off.
IMHO, have a urethane thumb slug inserted, and get the thumb re-drilled. You have just one material to deal with, and you will be back to normal standards.
I once had a ball where I also sanded too much and too deep, in order to get a smooth and deep bevel. But it was way too much, the ball slipped off of my hand. I tried to re-build the orginal hole with epoxy putty, but it was useless. I had to get another thumb slug, and since then I just carefully work on the bevel/upper end of the hole to get a good bevel shape for my needs. What's gone is gone, and it is VERY hard to repair such "damages"... Good luck!
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DizzyFugu - Reporting from Germany
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