Airport Extreme 6th Gens having trouble (one bridge, one router)

I have two brand new Airport Extremes that I'm trying to troubleshoot. The problem that I'm seeing is that occasionally one (or both) will stop functioning entirely on a weekly basis.

Details on our setup:

These are servicing a small business, generally about 40-70 devices are connected between the two. They are located apart from one another to maximize the reach of our wireless network.

One is set up as a router (DHCP and NAT), it is connected to a switch which is connected to a Time Warner modem that is serviced by our building's IT contractors (I do not have access to those devices as a result). This has led to us receiving warnings about a double NAT, which hasn't been a real problem for us but could a potential point of where these are breaking so I figured I'd mention it.

The other is set up as a bridge and extends the wireless network, so they are both broadcasting the same SSID. This was set up automatically upon installation of the device.

I'm only utilizing two of the router's ethernet ports: one goes to a switch that handles our non-wireless boxes. This issue has happened regardless of the switch's presence, though, as previously we just used the ethernet ports on the Extremes and had the same problem; the other goes to the bridge.

I'm curious as to what in the configuration may be causing this problem, because I'm not totally certain if it is the fault of the Extremes and possibly due to us using our own range of IP addresses with the . Usually it is the bridge that dies and it's a PITA to get working again - I usually have to power cycle both the bridge and the router to get the bridge to function again.

Thanks for any tips you can provide.