Netgear Access Point Slow Speed

 Hi, 

I am trying to setup my Netgear WiFi Booster Ex6120 access point which has been hard wired into my Netgear Nighthawk R7800 router with a Cat6 cable. 

However, the issue I am facing is slow speeds. I currently have 360MBs connection and when connected to the 5GHz Extender, the max speeds I am getting is around 40MBs download and 30MBs upload. The Internet connection on the Extender is performing much faster when over WiFi and not hardwired as an access point so Im not sure where I am going wrong. 

When connected to the extender when it has been hardwired as an access point, I also can't access it on my WiFi ext as I just get a "refused to connect" message.

Any help would be much appreciated.

Thank you