R7000 keeps losing internet

Hi, 

I have paired a Motorola MB7621 modem with the Nighthawk R7000/AC1900 Smart Wifi Router for my home network. My ISP is Xfinity and my plan provides for speeds of up to 600 mbps. 

I had no trouble while I was using the XFi modem/router for a couple months, but when I installed my own equipment I started having trouble with internet connection droppign randomly. The problem seems more pronounced on the 5 Ghz band (when connected I get around 150-200 mbps during daytime) than the 2.4 Ghz band (I get around 20 mbps during daytime but it does occasionally drop more in speed), but last night both bands went down and it took and hour and a hard reset of the router to resolve. 

It does not appear to be a problem with the modem itself, because when the wireless networks go down and I plug directly into the modem with a laptop to test, connection is fine and strong. 

The router is currently on firmware V1.0.11.110_10.2.100. I saw some threads suggesting a downgrade to V1.0.9.14_1.2.25, which I think i will try if there is another major outage, but I wanted to ask for help and see if anyone has any other suggestions on offer. 

Thanks for any help you can provide. I am happy to supply further details if/when needed.