D6300 as an Access Point

I use Telstra's Netgear DEVG2020 router as my primary Internet router. I also have a Netgear D6300 that I wanted to use as a second access point.

I configured the Access Point via Advanced Settings and using a 1 meter cable everything worked fine.

I then connected to the wall sockets and it failed. Pinging the main router was very intermittent.

I then set it up using the traditional method: DHCP off etc. Again it worked with a 1 meter wire but not when connected thru the wall.

I suspected my wiring. I desperation I got an old Billion BIPAC 7404 and set it up. It worked without issue.

I am convinced that there is something askew with the D6300's Ethernet ports as the run is only about 20 meters.

Ideas?