The resonator on the ZX120 may compress during shipping. If it seems short after first unlocking it, it may need to be flexed a few times. Grab the base of the ZX120 firmly in one hand, and hold the top of the resonator with the other. Stretch and compress the resonator gently about twenty times. The resonator should be around three-quarters of an inch tall when you’re finished.
The ZX120 resonator may also take some time to return to normal after being compressed for an extended duration. Let the ZX120 sit with its resonator unlocked for a few days.