We did an article that you may find helpful. This will guide you on how to improve wireless connection see links below.
Note: You may need make sure that the distance of the Main modem/router and the router is far from each other to avoid Wi-Fi interference.
Have applied the instruction however whilst LAN is giving reliable internet access from the extender/AP the WIFI signal is not reliable and drops out on different devices stating 'no internet connection'.
I applied the new IP address as per the TP Link instruction to the AP - with DHCP disabled as advised.
Any suggestions to improve WIFI reliability on AP?