Nighthawk M6 - VPN Drop outs

I have a client that we are using an Nighthawk M6 for connecting a small branch office to their main office via a windows vpn. The vpn is constantly dropping out every few minutes. Other branches using other forms of connection for the vpns are stable, so it is either something on the computer, the network, or the device. I would love input on how to troubleshoot this. Any suggestions are most welcome.