Hu is of course referring to the coupling between the feedback device and the motor .(usually on the rear of the motor, sometimes a coupler, sometimes just a set screw on the shaft)
If the coupler is cracked or the screw comes loose when the servo is commanded in the opposite direction the motor begins to move but the encoder does not. Since the feedback loops sees nothing the integrator continues to build until the motor (and screw) move far enough to move the encoder. Seeing motion the loop now stops the motor. This has nothing to do with how hard the machine has been used but will cause exactly the action described. Usually it will get even worse over time.
Check that the feedback device is rigidly attached.
Bob
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