@AdamC 

Good day,

Please try to change the wireless channel and channel width to see if it would help improve the Wi-Fi range:

And you could also consider adding the power-line adapters  to improve the Wi-Fi range If the whole house is under the same electric meter:

https://www.tp-link.com/home-networking/powerline/

Thanks a lot.

@AdamC 

Good day,

Thanks for your reply.

So, are you trying to say, if the client device is at the edge of the Wi-Fi range, MR6400 would lose the connection and require a restart?

Sorry, In the beginning, I thought it was the device itself that would drop the connection;

Is it limited to a specific device or any clients would do that?

By the way, how many devices that are connected to the TL-MR6400? And could you please give me the approximate distance of the Wi-Fi range, like how many meters?

Have you noticed if the internet and LTE signal light would turn off when the internet disconnected?

Thank you very much.