Look along the external sides of the handle housing. You will find multiple sets of holes. The spring clips lock into these holes, raising and lowering the height of the retractable handle.

Check the function of the mechanism by pressing the handle's button and watching the spring clips.

When the luggage handle is fully functional, the handle's button causes these spring clips to retract into the holes.

When the luggage handle is sticky or gets fully stuck, the handle's spring clips are not able to retract properly when pressing the handle button.