facing the same problem with zte ax226 modem.

try firmware upgrade.
if no luck, it could be compatibility issue, which is difficult to resolve.

I tried most by upgrading firmware but the real thing is that the modem is not host less modem. that means It's need user and password to connect the internet. So replace the modem with a hostless modem and wish it will be identified by router.
and if you want to share the internet with the zte ax226 modem the you need to share the internet by sharing from computer to router.