While it might be a faulty device be sure that you first do your best taking actions to follow all these best practices before troubleshooting any deeper (as bad radio reception due to interference and not having enough Zigbee Router devices will cause such or other symptoms) → Zigbee network optimization: a how-to guide for avoiding radio frequency interference + adding Zigbee Router devices (repeaters/extenders) to get a stable Zigbee network mesh with best possible range and coverage by fully utilizing Zigbee mesh networking