Have you checked the connection speed?
If your connection speed is 1Gbps, you would better contact TPlink support.

Identical situation. getting 500+ Mbps (up/down) over ethernet up to my c2300-- but LAN through the C2300 seems to max out at 65Mbps down, 5Mbps up. And similar maximums over 5ghz and 2.4ghz.

Some things to try... Power cycle everything (modem. router and PC (sometimes unplugging the devices from power is better), Use a different Ethernet cable as even new ones have been known to fail, use a different port on the router, try a different computer, be sure the WIFI is off on the computer when testing the LAN, bypass the router and connect the PC direct to the modem and run your speed test, router firmware up to date, PC drivers up to date, settings in PC set to gigabyte, IPv6 on or off, other devices causing double NAT such as a router attached to a gateway, NAT boost on or off, firewall settings, other devices attached to the router ports causing issues, and other things running such as cloud backups. Let us know what works for you.

see my reply at

https://community.tp-link.com/us/home/forum/topic/187958?replyId=476834

 

I noticed that the C2300 would slow way down (over ethernet or wifi) where I enabled any QoS or any device-priority (even to prioritize MY device!). Also seemed like disabling as much IPTV and multicast may have helped, but I'm pretty ignorant about any use for those-- we do not use any television devices or services.