ORBI LBR 20 wont automaticaly failover switch to mobile from wired when wired goes down

I have a 6 month old orbi that I bought new.

Its connected to broadband via Hybrid Fibre-Coaxial (HFC), my service provider is "Internode" (australia)

Theres no swich or anything in the way, its connected straight to the Broadband router

The Sim card for mobile broadband is connected to the australian optus network

Everything works fine. On both wired and mobile.

The issue is that when the wired connection drops out it wont automatically failover switch to the mobile. I have to manually reboot the Orbi to get it to do that.

When its on mobile and the wired network comes back online it automatically switches back, its just from wired to mobile that it doesnt do it.

i've checked and have it set to automatic failover on the admin page.

Any help greatly appreciated