4G LTE Modem LB2120 breaking the internet

Hello, 

I recently got the lb2120 backup and hooked it up to my network by connecting the modem to the WAN port in the device and connect the router to the lan port and I'm using it as bridge. My router model is netgear R6400. The problem is that the internet is going down from time to time.  I usually login to the wireless router and it seems like lb2120 stops passing public ip, subnet mask, and DNS from modem. and the problem then resolves itself after few seconds and it could take an hour some times. I checked the device manual and it seems like everything was installed correctly. Any advice?