@Blex Perhaps positioning the additional Deco node close to the main Deco, until it is setup?

  @yves_b thank you. I will try that...for longer

  @Blex 

Also, if you could explain what does it mean "The TP App does not "find" the new node even though it is pulsing blue and is visible to my phone" - how and where is it visible on your phone, if not in Deco app?

  @Alexandre. The App does not find it but I have scanned the QR code on the new/4th node and my phone sees it on WiFi . My phone connects but no internet.

  @Blex 

I see.

When I was adding X50-PoE nodes to my home mesh, I have found that when new Satellite is blinking blue, not Ethernet wired and is not far from Main Deco, and Deco app is simply open on smartphone - in a few minutes a message pops up in Deco app saying it has found another Deco unit and if I want to add it to Deco mesh.

Without me going through the process of searching for Deco unit in Deco app.

  @Alexandre. I wonder if a new satellite is actually discovered by the phone (app) or by the main Deco.

  @yves_b 

I can't tell for sure, but I think it should be an app on smartphone. Maybe bluetooth needs to be enabled on smartphone, maybe not. I think it is the app on smartphone, because process of adding Satellite should be similar to process of adding Main Deco when you do initial Deco mesh configuration.

I found that Deco app feature by accident. I had four X50-PoE and decided to remove one of them from Deco mesh to check WiFi coverage with remaining three. Left it blinking blue on the desk I was sitting at, had Deco app open to see mesh status, and then suddenly message appeared in Deco app telling there is new Deco unit and if I want to add it to my Deco mesh.

This is nice feature, useful for people not very familiar with TP-Link Deco, unless of course your neighbour is configuring their Deco mesh and you managed to intercept the process and hijack their Satellite Deco. :)