LB2120 LTE modem and router

[JonoR]

I'm wondering is some routers are just not compatible with modems like this?
I can connect the modem straight to my laptop and get internet, but when I connect it to the WAN port on my Dlink Archer D7 router it seems to work sometimes and sometimes not! I've tried many combinations of settings on both devices, but haven't nailed it.

I read a post somewhere saying that some routers don't support LTE modems... maybe this is my issue?

[plemans]

Make sure when your router is connected to the lb2120 wan port, that nothing is connected to the lan port. 

[JonoR]

Thanks for the input. Yes I've tried with nothing else plugged in a LAN port.