I call that "The Valley of Death". And - trust me - it is completely normal. Why... Pretty simple. When you start to work on a crack, you are completely inexperienced. You have no idea, no opinion and no clue. You just do it. And when it works, you try desperately to see, check and analyze each single step. Now it comes. Next time you try the same technique, you are no more spontaneous. You try to work from the list, you have in your mind. And that can't work.
Example. Tennis. You see the ball coming. You swing the racket and that's it. Next time you have a piece of paper on which you noticed every single step you need to hit the ball. Do I have to say that you'll miss completely, because you are more concentrated to read the technical instructions instead of simply hitting the ball...? When someone says that you learn when you do nothing, it should be: "You forget the plans you had in your mind, when you do nothing." That makes it easier for you the next time".
In other words: "The Valley of Death" means, that you try to reproduce the crack in your head, while cracking. And that will never work. Therefore I tell my students to think on something different, when they practice. Ask Jessie and Robert. They had lessons with me.
I have a screwdriver. I am Legend...