I have recently bought a TP-Link EAP-225 Outdoor to have WiFi in a garage that is no more than 10 meters from the EAP.

The 5Ghz network works just fine. The issue resides on the 2.4Ghz network. I can connect devices to the network, but speed drastically lows when I am around 10 meters from the EAP. Most of the time, I have no Internet or very low speeds (up to 500Kbps) at that distance.

I live on the first floor, and the EAP is placed on a wooden pole on the balcony and connected to the main router via a powerline. I have already tried to replace the powerline with another router working as a hotspot sharing device as a way to dismiss any potential interferences made by the powerline device. The issue persisted. 

At the garage, I am using a TP-Link RE455 to act as a range extender and spread the WiFi signal to the inside. 5Ghz works great, but I had to switch the 2.4Ghz off as I cannot take any benefit from it.

I have read some threads in this forum, and it looks this has been a constant issue to other users as well. I wonder whether there is a solution to fix it. I am fine with the 5Ghz network and the good speed, but I have some devices (mostly smartphones) that only work with 2.4Ghz.

I would appreciate some hints on how to solve the issue with the 2.4Ghz connection.

Thank you in advance.