Letting one part of your body race ahead of the others. (Most weekend players tend to power this shot with just their hands and wrists.) Try to swing through the ball as opposed to hitting it with your lower body constantly rotating toward the target.
Don’t worry—you’re not the only one who struggles in the super-short stuff. Shots from tight lies particularly pitches requiring less than full power challenge golfers at every skill level including many PGA and LPGA Tour players. And for good reason—these are really difficult shots with a really small margin for error.
Most amateurs spend a big chunk of their practice time on dead-flat practice-range tees. They seldom practice from long greenside rough sand bunkers side-slopes or uphill and downhill lies. And I understand that. Why practice from difficult lies when you can’t even hit good shots from good lies?