@David-TP 

Thank you for your reply.  Yes both Deco M9plus has the same issue. Deco are in the same place than before, location has not changed

  @rmoronf 

For two Deco units, you can just connect them by Ethernet cable. Is that what you had?

If you added more Deco units, perhaps you added a switch, or replaced switch you had with new one? If wired correctly, Deco Ethernet backhaul should work regardless of what different types of Deco units you connect together.

It would help if you could draw network diagram, with how each Deco unit wired and where, and tell if you run Deco in Router or in Access Point mode. Also see this document for Ethernet backhaul discussion: General questions about Ethernet Backhaul feature on your Deco

  @Alexandre. 

Hi,

I attaching a diagram on how I have my mesh network.  It is exactly the same I had before, just add one more DECO replacing one of the M9plus as main with the DECO X20.  Same cabling, same swith (netgear).

Leds sometime are flashing red and then goes to green keep swithing state during the whole day but WIFI signal is OK.  Same thing happen to both M9plus, the one connected by wifi and the one using ethernet cable.

A video showing how led is performing also attached.

Regards

Ruben

  @rmoronf 

For troubleshooting purposes, consider eliminating Netgear switch temporarily, to verify if it causes the issues. I do recall having conversation with someone who found issues caused on their Deco mesh were caused by Netgear switch.

Either totally remove Netgear switch from the picture and have your wired link between X20 and M9Plus changed from this:

Deco X20<---Ethernet cable-->Netgear switch<---Ethernet cable-->Deco M9Plus

to this:

Deco X20<---Ethernet cable-->Deco M9Plus

or, if there are wired devices connected to switch you don't want to lose even while testing, this can do, too:

Deco X20<---Ethernet cable-->Deco M9Plus<---Ethernet cable-->Netgear switch

Once again, this is temporary change for testing purposes. If after that change Deco mesh stabilizes, it proves the cause of Deco mesh issues is indeed Netgear switch.