For Google wifi, it won't work if you connect it directly to the Arris as NBN HFC requires a VLAN which google wifi doesn't have.
You may use your google wifi as a router or wireless repeater together with our TP-Link VR1600v which has the VLAN that NBN Requires.
Please try the follow my recomendation below.
After saving turn off your google wifi and connect it to our TP-Link VR1600v Router
Make sure you use the WAN Port of your google wifi.
Turn your google wifi on and try the internet
Let us know if this work.
I responded to your initial post located here. https://community.tpg.com.au/t5/Broadband-Internet/FTTB-super-slow-TPG-speedtest-exaggerates-actual-...
We'd like to set your expectation that we do not have any information on how to setup Google Wi-Fi. In the event that you require assistance we recommend to contact the manufacturer's support.