I was going to mention Rick Ankiel as well. I thought I read something that talked about this psychological block and referring to it as some sort of sports performance anxiety. I'm not sure if that is the exact name for it but it plagued me as a shortstop for a couple of years (16-17).
It's like you're afraid of the baseball and when you get it all of those bad throws flash in your mind and you begin to worry. You hold onto the ball a little longer than normal and when you go to release it you either do so too soon or too late.
I'm not really sure how to get rid of it. I believe there are people that specialize in treating it and I'm sure you could find a book on it.
I got rid of it by just taking a lot of reps at shortstop. Really focusing on fielding the ball, getting my feet right, and throwing it to the target. Having sort of an arrogant attitude about hitting the glove. What I mean by that is creating a feeling that when I release the ball I KNOW it will end up where it was intended to end up.
Very difficult to shake. Good Luck!
Jason