@David-TP I could be wrong but my understanding is that QoS packets are used to monitor and manage network traffic and so the Deco app is probably using them to generate its maps and manage the devices. Plus I note that a QoS fix was the only change in the latest firmware update.

The wifi continues to work well by the way, the app continues to report that the network is not functioning (apparently incorrectly).

  @David-TP Hi,

The powerline models are AV600.

The app is inconsistent. Sometimes it reports everything is fine but within a few seconds it then says the main deco isn't working.  Sometimes it reports some of the satellites as not working, but I can click and see connected clients. I emphasise that the wifi appears to be working perfectly now from a user's POV. 

I think it is probably a problem with the Decos reporting to the App correctly, which may be a QoS bug.

  @David-TP It doesn't matter to where the the other satellites are connected to or not. All my M9 are connected to my main M9 via Ethernet, also all of my m5s are connect through Ethernet except one. my X50-outdoor will never connect to the preferred M9, the closest. All many others here are experiencing. It's just your R&D whom cannot reproduce. It's a pity.

  @nickname125 i have reset the "satellite 2" deco and it still cannot be added to the network. Either in it's original position or next to the main Deco. The setup process seems to work, it says it has been added successfully, but it continues to show as offline in the app. Connecting it via ethernet seems to allow it to show as connected in the app but then Satellites 1 and 3 are shown as disconnected... however the wifi does appear to be working. Perhaps it is an app problem.

  @David-TP 

The network map is:

ISP Router -- switch/hub -- main deco

\ <wireless> -- satellite 1 -- <wireless> -- satellite 2

                                             \ --<ethernet>-- satellite 3

\ <ethernet> -- satellite 4

Satellite 2 will not reconnect. The Main deco doesn't have an ethernet symbol in the list but satellite 4 is connected so I guess it is working. Satellite 3 should be ethernet but is currently connected by wireless with a very weak signal (i would actually prefer this configuration but the signal is weak and not stable enough).

The switch/hub is a tplink SG105. I have swapped it for another unbranded chinese one and it seems to behave the same.

(The two ethernets are different powerline networks with tp-link adapters) 

I will submit the log now.

Update: while the wifi seems to be working ok (minus the deco that won't connect) the Android App always has the error "Can't connect to Deco" when it starts up, except I can click on each Deco and see its details and what devices are connected.