Your massage gun could keep stopping on its own when it’s overheated to protect the device’s integrity. If the device is overheated, make sure to give it a rest in intervals between usage to let your massage gun cool down. If the device stops working and does not overheat, the problem would be its interior parts. You can ask a competent electrician to pry open, inspect, and repair your massage gun’s internal components. Make sure not to try and fix the massage gun on your own.