Motorcycle paint help

I am repainting my motorcycle with some spray cans and I have painted the tank, front fender and rear fender pieces all with the same primer, same color, and same clear coat successfully. A little bit ago the side of my tank got some cosmetic damage so I sanded it back, re-primed it, re-painted it and then coated it with the same exact clearcoat that worked the first time and it cracked on me. I figured that I had some type of surface contamination that the clear didn’t adhear to so I sanded it back and re-primed and painted then cleaned and degreased it only to have this cracking happen a second time. Third time I repeated the same steps but then sanded the color lightly with 1000 grit to try to give the clear topcoat something to grip. Then I, again cleaned and degreased it to a point you could eat off it and this cracking happens again! Any help would be greatly appreciated as I’m at the point I’m wanting to sell my bike this is frustrating me so much.