@Cazza1 

It is valid recommendation to make M9 Plus your Main Deco. You should do that.

Also, the rest of M9 Plus should become backbone of your WiFi mesh, with M5s extending WiFi from M9s to further places of your house. We can discuss proper layout of Deco later, if you are interested.

Having said that, it is known issue for M9 Plus on very old firmware to incorrectly report where devices are connected. This old firmware can't be updated through Deco app. To find if this is what you have, make screenshot of "Update Deco" page from Deco app and post it here. 

I'll guide you through firmware upgrade process for that special case. That upgrade might also fix your security camera WiFi connectivity issues. It will also bring very many useful features.

Example of Update Deco page from Deco app that I'll be waiting to see from you:

  @Alexandre. 
 

Hi- 

many thanks for your replies.

i swapped the main node- it's now one of the three M9s. no worse in terms of wifi, but still appears that all the devices are connected to that one node, and it's still not reaching the back camera.

here is a screenshot of the nodes we have. Thanks, I'll be interested to know if it's possible to improve my system without having to buy a whole new, more up-to-date system.

  @Alexandre. 
Thanks for this, I'll try it today.

Should I turn off my two M5s while the update is happening? 
Should I move the three M9s closer together while it's updating too?

  @Alexandre. 
 

I've done the update and now the app is SO much more informative. I can now see the signal strength of each node, and which devices are connected to them.

I've switched the nodes around and repositioned them, and all now have strong or medium signal strength!

Thank you so much for your help.

Just one last thing: I tried to give my two M5s (EU V3) an update too. I downloaded the .bin files for versions 1.7.4 and 1.7.5 but I couldn't see how to install them - there was no wizard/upgrade tool

Should I use the one for Version 1?

Thanks again xxx

  @Cazza1 

Congrats! You now have up to date Deco WiFi mesh, with a set of new useful features. Among them, I recommend you take a look at the following: Connection Preference: Customize Your Preferred Signal Source and How to select a preferred signal source on the Deco App

I suggest not to update M5 manually. Use Update Deco in Deco app from now on: it'll make sure the right firmware is offered for the right hardware. If you don't see firmware 1.7.4 and 1.7.5 in Update Deco for M5, it may be because TP-Link hasn't pushed it yet to wide audience, collecting info from early adopters. There had been once or twice on my memory when TP-Link had to recall and redo firmware update, so it make sense to wait till it appears in Update Deco page.

Comparing to firmware 1.7.3. you have with M5, 1.7.4 and 1.7.5 will not bring new features. This update can wait.

Do you still want me to spend time with you on tuning your Deco mesh, or you will be doing it by yourself? If you need my help, a lot of questions from me will follow about your network layout, Deco units placement, etc.

  @Alexandre. 
 

Thanks - I'll leave the M5s for now 👍

Re the positioning, you said use the M9s as a backbone, so I've linked them in series, with the M5s connected to the main (see map).

But I actually think it was working better when the M5s were in the Library and Kitchen.

Should I revert? The security camera that we're having trouble with is on the back outside wall of the Kitchen... Thanks.

  @Cazza1 

Deco M9 Plus is tri-band and more powerful in hardware and WiFi signal than M5. I have both models, tested them extensively. When you do daisy chain Office<->Library<->Kitchen with M9 Plus, you should get better results than with M5. 

With M9 Plus in daisy chain, your Library and Kitchen Deco will deliver faster WiFi speeds than if it were M5s, and difference should be noticeable.

As for M5s, ideally you connect them to M9 Plus that is on the same floor, but if it is bungalow - perhaps the way you did it. You see, without house layout/floor plan and Deco units location it is hard to tell if M5s are connected optimally. In any case, they should be connected to M9s as sort of M9 extenders to where WiFi does not reach from M9 Plus - and on the same floor of the house as M9 they are connected to. 

If we to continue this topic, I'll need to see floor(s) map with Deco units (including their names) and router and security camera. 

If you think you had better performance with M5s in the Library and Kitchen, feel free to try. With "Connection Preference" feature your Deco mesh now has it is easy to play with Deco mesh layout to find what works for you. 

-----------------

In regard to security camera. Where and how is it connected now? If you can give that info, it may help to figure why it can't connect to Deco mesh and we may be able to find workaround.

Devices such as security camera often fail to connect to WiFi mesh (any brand of it) for the one of the following reasons:

1. Security settings of WiFi connection;

2. SSID/password with special symbols;

3. Multiple WiFi nodes (mesh units) broadcasting same SSID/password;

4. Dual band: same SSID/password for both 2.4GHz and 5GHz band.

The last one is most common.