D7000v2 no internet connection with Nighthawk MR1100

I have a D7000v2 system running as a WiFi router configured for internet access via its WAN port i.e., I am not using the ADSL modem.  The WAN port correctly provides internet connectivity when using a separate WiFi bridge device -- so I believe the D7000v2 is working fine in general.  However, when I replace the WiFi bridge device with a Nighthawk MR1100 (4G backhaul) no internet connection is ever established.

The MR1100 is configured in IP passthrough mode with DHCP disabled.  I have confirmed that the MR1100 works correctly when connecting it to my PC's LAN port.  I am getting an internet connection independently through the MR1100 and my PC is able to access the internet via the MR1100 ethernet port to the outside world.  The problem is that the D7000v2 and MR1100 don't appear to play nicely together.

I can see that the D7000v2 has obtained the correct internet IP address from the MR1100, so at least some part of the connectivity is working being these two products.  Even the internet green LED lights up on the front panel of the D7000v2 suggesting there is an internet connection.  But, bizarrely, the home page of the D7000v2 indicates "no internet connection".  My PC also has no internet connection when attached to the D7000v2 WiFi so the problem seems to be with the D7000v2/MR1100 connectivity -- the Internet Port statistics on D7000v2 suggest very few packets are being exchanged which seems to suggest there is a protocol issue or packets are getting dropped.

Does anyone have any experience with this particular combination of products?  If so, how were you able to configure them?

My ultimate goal is to use the MR1100 in IP passthrough and use the D7000v2 as a VPN server to get external connectivity onto our private WiFi network.