LM1200 repeatedly dropping link

Sorry to add to the pile, but I am dealing with this exact issue and am hoping a resolution is close. I am in a rural location with only a single Verizon cell tower accessible, so I have no other options than to get this working somehow. I am using an LM1200 with a verizon provided SIM card, in bridge mode (after reading through the previous entries). I have an EnGenius EWS850AP connected for my WAP. When the system is running without a reset (for anywhere from a few tens of seconds to maybe half an hour) I can get net access through the wifi to my laptop or my cell phone. When I try and actually hook up the devices I need at this site (security cameras and miscellaneous controllers for items like heating systems) I can't successfully connect to the source router. I take that same WAP to a different location and connect it to a DSLAM, I can set up my devices just fine, which tells me that either my configuration on the LM1200 is incorrect, or somehow Verizon is filtering the IP traffic so that only a cell phone or a laptop PC can negotiate the connection.

any advice is welcome. I don't have the specific IP transport knowledge that many use here, but I am a 30 year veteran digital hardware designer and at least familiar with the basics.

Same here, actually with a Ubiquiti USG (Unifi Security Gateway).

Verizon 4G SIM, BYOD w/ a public static IP, 

I got the LM1200 in bridge mode, have the USG configured properly, but the moment it attempts to use the LTE network, which 99% of the time it will never actually establish a connection.

If it does actually connect to the LTE network, it will only for a brief moment, then seemingly "restart" where you lose connectivity to the webpage AND loss of internet. So I can only assume the device is restarting itself. It will repeat this forever, but if you let it remain disconnected from LTE, you can login to the device and play with settings, it's just actually connecting is where it stops working.

This is using the latest Unifi Controller, USG firmware, and latest Netgear firmware. Even after factory resetting it and just putting it into bridge mode, no dice.