@Roy-B 

Your edge node, is it connected to hallway node, or to main Deco node?

@Alexandre. 

I can see the 2 Deco units are connected to the living room.Can I change it?

@Roy-B 

You can not change which node Satellite node connects to, at least not in current X20 firmware. See TP-Link article on that topic: [Deco] Manual Signal Source Selection

Scroll down to the bottom of it for FAQ articles that might help.

@Roy-B 

On second thought, can you run one more test? Power off edge node in home office room, and from that room run speedtest with mobile device that is now connected by WiFi to one of two remaining decos.

It may sound counterintuitive, but you might get better speeds with that setup. Worth checking.

@Alexandre. 

It was interesting test,and I will give more details.

I have disconnected the deco in the home office and tested it from my phone,it got connected to the main unit and now I got 135M download(which is great for my needs).

The issue is that my laptop is placed in a spot that it can't reach  the main network.

What is your advice?

@Roy-B 

That speed test result tells me your home office edge X20 may not be placed optimally. While Satellite X20 covers your home office with strong WiFi signal, its connection to Main Deco is weak and this is where you lose speed. 

I am somewhat confused with location of your laptop. Is it not in the home office? If it is, does it mean your home office is so large it has WiFi dead spots? Because, you know, for a "regular size" home office room to have 135Mbps in one place and no WiFi signal in another place is somewhat puzzling.

To help me help you in troubleshooting, would you please draw your house layout with X20s placed in it. Label which one is Main and which are Satellites. Show where did you run speed test from when you powered off home office Deco. Show where your laptop is located in your house.

Also, would be nice to see where WiFi dead spots are when you power off home office Satellite Deco. 

Also, please answer the following questions:

1. Do you run your Deco mesh in Router mode or in Access Point mode?

2. If you run your Deco mesh in Router mode, is it because you have to, or you just left Deco mesh in its default configuration for Operating Mode?

3. Is your home Internet coming from TV cable, or from fiber, or from something else? 

4. If your Internet is on TV cable, what is brand name and model number of your ISP router?

5. Do you have TV cable outlet in the office room?

6. Do you have TV cable outlet in close proximity to laptop?

@Alexandre. 

1. Do you run your Deco mesh in Router mode or in Access Point mode?Router mode

2. If you run your Deco mesh in Router mode, is it because you have to, or you just left Deco mesh in its default configuration for Operating Mode?
At the moment the main Deco is connected to fiber to rj45 adapter no switch between it.When I tried to move to AP the other nodes did not start since no router is connected(per my understating) 

3. Is your home Internet coming from TV cable, or from fiber, or from something else? Fiber

4. If your Internet is on TV cable, what is brand name and model number of your ISP router?N/A

5. Do you have TV cable outlet in the office room? I do

I have attached my home sketch,red circle is the main deco(fiber connection is there) ,2 blue circles are the edge deco nodes,green is where my laptop is located.

I hope it's now clear.

When I tested the speed with my phone it was in the middle of the room and not from the laptop location(did find the wifi network in that spot,yes it's probably a dead spot). 

@Roy-B 

Thanks for the picture. It is clear for me now what you have.

It is also clear why your laptop won't get WiFi signal when you turn Office Deco off as I asked: too many walls between it and remaining Decos.

Also, I think I understand the Internet setup you have: ISP provided you with fiber modem and you must have your own router. Main Deco is your home network router. With that setup, you can't run Deco in Access Point mode. That reduces flexibility of Deco deployments, but there are still options.

I have three options for you to consider:

1. Accept what you have now, run 3-nodes X20 mesh, and wait till TP-Link releases firmware 1.6 for X20. With firmware 1.6 you should be able to tell Office X20 connect to the middle Satellite X20, instead of Office Deco connecting to Main Deco. By my estimate, that may improve WiFi speed in the office from 40Mbps to 70-75Mbps.

Note that it is unknown when firmware 1.6 for X20 will be released. Could be soon, could be many months.

2. Replace 3-nodes X20 with 2-nodes X90. Deco X90 is top of the line unit with WiFi backhaul (connection between nodes) much stronger than X20s have. Deco X90 is way more expensive than budget X20, but you may be able to find 2-unit X90 set for about the same price as 3-unit X20 set. 

If your X20s are still within return window, consider that option. With 2-nodes X90 set, place Main Deco X90 where your current Main Deco is and place second unit, Satellite X90, in the Office where your Office Deco currently is.

If it works, I estimate you may be able to get speeds up to 100-120Mbps in the office, but it might not work. Only practical test can show if two X90s better than three X20s you have. Which means, this could be multiple steps: try two X90s, if they don't deliver - return them and go back to three X20s. If X90s do - keep them and return X20s.

3. Because you have TV cable in your office, you may consider setting Ethernet over coax (TV cable) and connecting Office X20 to Ethernet connection. It is called MoCA, you may need to research that topic (i.e., Google it). This is the basic scheme:

You will need a pair of MoCA adapters, at least version 2.0 or better (look for gigabit in description). If you had cable Internet, your ISP modem most likely supported MoCA protocol and you would have only needed to add one adapter. With what you have, you'll need pair adapters, both of the same brand, type and model.

With MoCA adapters, connect one of them to Ethernet port of Office X20. Another one must be connected to second Ethernet port of Main Deco - hopefully you have another cable TV outlet nearby and can pass Ethernet cable from cable TV outlet with second MoCA adapter to Main Deco.

Alternatively, you could connect Office X20 with that to your middle Satellite Deco, if there is more conveniently located TV cable outlet near it. This will bring less speed benefits, but will improve WiFi speed in the office nevertheless.

If it works and Office Deco is connected through MoCA to Main Deco, expect same WiFi speeds in the Office you are now getting from devices in the living room connected to Main Deco: 450Mbps.

If you need to connect Office Deco to Satellite Deco that is in the middle of the house, I estimate you should see at least 130Mbps in the Office.

This may or may not work, depending on TV cables layout in your house and if MoCA adapters are compatible with Deco Ethernet backhaul protocol. They should, but you never know.

My point is, if you invest in MoCA adapters, get them with return policy of at least few weeks.

@Alexandre. 

First,Thanks for you help!

I have just checked the X90 is not available yet in my country(I am not from the US). 

I do have a tp-link wireless router here VR600 that I can connect before the main Deco and change the setup to Access points,Do you think it will help?
My second option (less convenient because of the TV spot) is adding cat6 cable that will reach the office room and than connect the satellite deco to it.