That is really odd.
Try opening a new file and appending in the models. That can fix odd bugs from accidental strange key presses for example.
I would check your mesh in the neck of the pin.
do you have hidden geometry?
more then one mesh object in your pin?
i think it’s an Eevee shadow configuration problems. like shadow clip start 1.4 m?
Try rendering in Cycles is shadow is good, then check shadow related properties for eevee.
That looks funny but did you check where the problem was? Was it with Eevee or the mesh?