Yea bro, I can relate! I stutter while speaking, but it also can happen physically. For example, before I use a spray paint can, my finger often freezes up before I finally press down. I believe my body naturally freezes me because I’m afraid to make a mistake with the can and over-spray. I think maybe you have a fear of making mistakes in your piano playing. Or you’re just not living in the moment, so it’s inhibiting your “flow”. Good observation though!