Why does the throttle go on and off when the wheel is raised?

Your bike is programmed to have a smooth assist with the throttle all the way up to 20mph. When you raise the wheel from the ground and push on the throttle, it is freewheeling and it immediately goes above the 20mph limit so it stops the assist and then it waits until the speed is closer to continue giving power. This is not noticeable while riding as the weight and torque will keep it constant, but when freewheeling you can see this as normal behavior.