Are you facing intermittent connection issue using direct connection or the issue is happening only on the Wi-Fi connected devices?

In Wi-Fi both the networks are affected 2.4 and 5G as well or only one?

when the internet drops did you noticed the LED on the modem is going off or changing color or flashing?

I lost internet through both WiFi signals and wired connections. Multiple times daily. Only resolve is manual restart. No change on LED until restarted.

Since you are experienced with both wired and wireless intermittent internet connection, I would suggest checking the cable signals to make sure all the signals are in range.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Cable-Signal-Levels

My cable signals are good. I don’t have this issue with 2 other routers/modems that I have. It is a device issue. 

If you tried with all the possible troubleshooting steps, I would suggest visiting www.arris.com/consumersupport for further assistance.