Motorola Solutions — Auto restarting problem in moto e 1st gen

Address:

700091

I am using 2 Moto E 1st generation since it has launched. It was working fine without any disturbance. But suddenly both the mobiles have started restarting automatically while pressing the power key to unlock it. It's happening almost every time I am pressing the key. As this is happening with both the sets I am bit worried. Can you please explain if this is a manufacturing defect of this particular model or something else ?