@schillkroete Consider upgrading M5 to latest hardware firmware, as a first step. You may need to do it manually, by downloading it from TP-Link Web site of your region. It might be possible that...

@ESIntegrators This document may help: How many Deco units can I add to my Deco mesh network?

@another123 If you want to keep Deco parental controls, that would mean running Deco in router mode. With that in mind, I am going to simplify your picture, leaving only relevant to your quesiton...

@kenlag It is recommended to turn off WiFi on existent router after Deco mesh is deployed. Deco does not extend existent router WiFi network, it creates own WiFi network. If you keep WiFi on at...

@Pharoahe9 I am assuming you have Main Deco M5 and two or more Satellite Deco M5, correct? If this is the case, one simple test you can do is take problematic Satellite M5 and swap places with...

@drazgo Activate guest network isolation, wait for about 5-10 minutes, then check if you have access to LAN from Guest (you shouldn't). When I tested that on my Deco mesh with M9s, I have found Deco...