SURFBOARD SBG7400AC2 MODEM/ROUTER WON'T STAY CONNECTED

Since you have a gateway, you need to first isolate if the issue is wired or wireless. The best way to do this is to see if the LEDs on the front began flashing when you lose connection. If this does happen, then the issue is with the communication between your ISP (service provider) and your gateway. The most common cause for this issue is the signal levels being out of range or close to being out of range. Check out the link below for more info on signal levels. 

https://arris.my.salesforce-sites.com/consumers/articles/General_FAQs/SBG7400AC2-Cable-Signal-Levels

You can do things like removing splitters that you don’t need and making sure that all coax cables are tight to help with this. If those things don’t help, you would need an ISP tech out to your home to help, this isn’t something that they can fix over the phone. 

If the LEDs stay solid when you lose connection, then this points to a wireless interference issue. This is usually caused by the Wi-Fi channel being too congested by other networks. A simple reboot can help with this as your gateway will search for the least congested channel after the reboot. Other things that can help are:

• Placing your gateway in the center of your home 
• Don’t put it behind any electronics or appliances
• Don’t put it too close to cordless phones (landline not cell), baby monitors, or your microwave
• Make sure it’s not behind a metal or concrete wall as the signal has a hard time going through them

Let me know if any of this helped or if you have any questions.