The main cause of random reboots and disconnects at USB powered gateways is the inadequate source of electrical power.
Check the USB cable and the DC power supply. We recommend that you always use the original USB cable provided with the equipment. If you do not have the original cable, use a 2A rated shielded cable with a maximum length of 1 m (30 feet).
Please read this article also: What are the DC power requirements for the IoT gateways powered via USB cable?