Netgear M2 Modem mode plugged into a Huawei AX3 Pro

I leave my huawei ax3 pro in router mode. I then put my netgear nighthawk m2 into modem mode (ip passthrough on, dhcp server off). Then I connect the m2 to ax3 pro via ethernet. I have internet for about 10 seconds and then the m2 loses its mobile data connection and starts searching for a mobile network. It does not regain mobile data connection until I remove the ethernet cable. Any ideas on whats going on?