The new LTE Router IS the bridge. It’s an Zyxel LTE7460 which takes the SIM card and the router is then placed in Bridge mode allowing the USG to take care of NAT, DHCP etc.

The E3372 is no longer needed as the Zyxel does everything.

The problem with the AR150 was it wasn’t taking the public IP address from the E3372 which it should do. It wasn’t bridging the connection between the E3372 and itself otherwise it would have obtained the public IP.