Lb2120 cant see wireline

purchased 12 May 2021 so check to see if its faulty unit or doesnt work the way i thought it did

So from my reading i thought i would sit between modem and router and swap to 4g if virgin goes offline

My setup

{internet} >Virgin hub3 modem mode > Wan port LB2120 bridge mode [tested router mode also] lan > Archer AX1100 router > other suff 

if i remove the LB2120 everything else works fine

I've removed to sim card whilst testing but it makes no different either way

The fail over tests for my isp dns, ive also tried googles dns and my VPS no difference 

I've tried factory reset, all ports on the v3 hub and fresh cables.

my question is am i missing something or do i have a faulty unit ?