Studies show that force production and muscle activation decrease in the second half of the positive portion of a bench press rep. This is due to the fact that the vast majority of reps performed during training are aided by momentum during the second half of the press. Therefore, during a max bench, many people get stuck at the halfway point since they’re not used to producing more force in the second half. Use exercises like board presses or triceps isolation movements to improve the second half of your bench press and increase your max!
Source: Elliott, B. C., Wilson, G. J., & Kerr, G. K. (1989). A biomechanical analysis of the sticking region in the bench press. Medicine & Science in Sports & Exercise, 21(4), 450-462