I also have this problem, I am using Tower Pro Micro Servo 9g SG90，
After the square is recognized again, the translation servo motor will tremble. The tilt servo motor runs in the opposite direction to the ideal state. The square is above the window and the servo motor moves downward.
Hi Ke Chen,
it sounds like the servos are reversed where they plug into Pixy. Please try reversing the plugs - that is, plug the tilt servo where the pan servo is, and plug the pan servo where the tilt servo is.
Hope this helps!
Cheers,
Jesse