@David-TP  The Deco P9 are set-up in wireless router mode. the first Deco is attached to the router from the ISP.

The Deco was initiated into the network close to the primary Deco. then moved to the desired location. Adding the fifth has created instability into the network.

I am haveing issues with upploading photo:

Here are the screenshots you asked for:

https://www.dropbox.com/s/k7a5wsucu7retkg/Deco%20CA%20grafic%20overview.jpg?dl=0

https://www.dropbox.com/s/no1b5fn51893xcd/Deco%20CA%20line%20overview.jpg?dl=0

  @Reinea I used P9 in combinaition with anything thrown at it but the kitchen sink.

My experience with P9 is that you need to be in full range of the other either with a wire, or close towards other Deco's showing in the app that is is connected as strongly as posible. (As in backhaul the red light issue, it needs to be connected either with a wire direct to your main p9 with nothing in between..)

So first create something solid then move it towards the position at that time, one at the time. (sometimes I tested for a week to see if it was stable)

I have a setup that is 500M2 (So that may take some time..)

If you move towards the next floor like shown in your setup the third floor you have to make sure something solid is grounded to cover your third.

If you expect it to take it from the second because everything was working, it probably is the guessing game that will not workout as intended. (Unstable at best most of the times)

Eventhough a P9 may show a strong wireless connection(which is good ofcourse), it must be said if the backhaul cannot run back straight towards your main (router) P9 Deco it will start to go red light(so make sure it can make that straight line as intended.

In my case I had to increase the power connection cable to make the best connection towards the other (wifi nearest, strongest link) (the original is rather short).

Anyways take care.