@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,...

@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

I used to have a mesh network with 2 deco M9plus working fine, connected by ethernet wire. I decided to add a new Deco X20 as I have now some smartphones and laptop with WIFI6 and changed the main...