R6700v2 unreliable networking

I just replaced a Linksys AC1750 router with a Nighthawk R6700v2 with the V1.1.0.38_1.0.1 firmware.

I have two computers running backups to a network attaced hard drive.  One is connected via a cable and the other is wireless.  They are copying sevearl hundred gigabyte files across the network to a network-attached hard drive.  Both devices will lose their connection at the same time, about an hour and a hald into the transfers, and I have to wait about 30 seconds or so for the network to come back up.  If this was a cheap Belkin router I'd expect that sort of behavior and say I was just driving the CPu too hard, but for a router in this price range I would certainly not expect the wired networking side to drop.  I have restarted these transfers several times and they have never completed.

Is it normal for this router to be incapable of staying up long enough to finish a couple hundred gigabyte transfer over a gigabit wired Ethernet connection? Do I need to just put the Linksys back or should this work?