Model : TL-WPA4220KIT

Hardware Version :

Firmware Version : 2.1

ISP :


Hello

I have the AV600 WPA4220KIT and the TL-WA850RE and I am still struggling to have a good connection.
The apartment is fairly long and I have attached a pictorial representation of my house. It's around 65ft/20m long and the router cannot be moved.

The extender is wired to the router in the living room, and the other one is in the middle of the house. The house icon does light up, all 3/4 (no ethernet).
The speed when restarting the poweline adapter is good for the first 5minutes and then shows as "no connection".
I have even added a further wifi extender to improve the connection to the bottom bedrooms but nothing.

What do you suggest please?