@abhishekgujjar 

Please check the hardware version of your M4 units. If it is hardware V4, TP-Link provided solution for it: https://community.tp-link.com/en/home/forum/topic/581554

ImtiazAli wrote

One deco must be set up as "main" Deco, and other units will work as "satellite" Decos in the network. All satellite Decos will connect only to the main deco.

  @ImtiazAli 

This is not exactly correct, there are nuances. Satellite Deco prefers to connect to Main Deco. If signal from Main Deco is very weak or non-existent, Satellite Deco will connect to another Satellite Deco.

TP-Link started to release firmware that allows to overwrite that preference. With that firmware, user can define where Satellite Deco should connect. Deco M5 has that firmware released for general public, Deco M4(V4) has that firmware in beta currently. 

I expect that eventually each supported Deco model will allow user to define Satellite Deco connection preference.

  @ImtiazAli 

Sure, no problem.

 @abhishekgujjar 

Please check firmware hardware version of your Deco M4s. If it is V4, you can follow link I provided. If not, there may be workarounds available but I'll need to ask you more questions about your Deco mesh before I can be sure.

  @ImtiazAli  I don't agree it supports only star topology, even while adding a new Deco it asks how is it placed (1floor, 2 floors etc). And in the options provided it includes both mesh and star topology.

Regarding how many Deco M4s I have, it's my wish, why do I need to justify it, I've purchased them and they should work the way they are supposed to, period.

  @Alexandre. 

Thanks for your inputs. Below are the firmware details, can you advise how to proceed:

Please find 

  @abhishekgujjar 

Thanks for sharing this screenshot. It points at possible inconsistency between firmware versions of your Deco nodes, but I'll return to it later. What I need you to find for me is hardware version of your Deco nodes. I made a typo in previous post, but I fixed it now - hardware version is what needed.

Because you do have different firmware versions, you might have different hardware versions, too. To find what you have exactly, I need you to login to Deco web management interface and share screenshot with me, I'll tell you which one.

If you run Deco mesh in its default Router mode, you can login to Deco web interface through http://192.168.68.1 

Enter the password of your TP-Link ID to log in.

There, select Advanced at the top. Then, choose System/Firmware Upgrade. Wait till Online Upgrade screen populates on its own (could take few seconds), make screenshot and share it here.

Here is example screenshot from my Deco mesh:

In this example, I have two Deco M9 Plus with hardware version 2.0 and two Deco M5 with hardware version 3.0.

  @Alexandre.  Thanks for your inputs, please find below. lliving_room is the main deco, which along with bedroom and Dining was the initial set of 3 decos I bought. master_bedroom deco is the single deco I added recently to the network, and master_bedroom needs to connect to the bedroom deco, which it does initially and gives a good speed, but eventually it switches to the main deco living_room and then it becomes slow.

  @abhishekgujjar 

You have exactly what you need!

Your master_bedroom Deco is hardware V4 and you need to have ability to configure just that Deco where connect to (to the bedroom deco).

Here is the process:

1. Update master_bedroom Deco to beta firmware 1.1.0 following instructions from this link: https://community.tp-link.com/en/home/forum/topic/581554

Keep all other Deco on their current firmware.

2. After you successfully updated master_bedroom Deco, open its page in Deco app, touch text "Signal Source" and new configuration window will open where you can configure preferred connection.