@vDex Thanks. I have better picture now, screenshots are easy to read. I notice you have Main Deco and one of Satellite Deco with the same name "Couloir", I did not know it is possible to give two...

@NickDems I would say, these logs lines you should be concerned with: Sun Feb 26 19:21:55 2023 daemon.err miniupnpd[18139]: Failed to get IP for interface br-wan Sun Feb 26 19:21:55 2023 daemon.warn...

@vDex Thanks for screenshots. From your initial post I assumed you only have two Deco: Main and one Satellite. Your screenshot shows four Deco in total. That is important information for...

@arnonm Before discussing what might go wrong with Main Deco in AP mode, I want to say that it is usually OK to run Deco mesh in Router mode, even if it is connected to ISP router. There are very few...

@devilson911 Start with the following TP-Link document: General questions about Ethernet Backhaul feature on your Deco

@vDex If you can tell what speeds you are getting with device connected to Main Deco P9 and what speeds - when connected to Satellite Deco P9, that will help to figure what does "very big loss" mean...