@TP-Link I will try and feedback later. After setup from wireless backhaul, wired in and it works normally for like a minute (app is showing clients and connected to the main unit via ethernet), then...

Swap the device, same problem. Tried reset both of them, now the satellite gets an IP from DHCP but cannot setup (blinking blue led) when wired to the modem. It can be setup if using wireless...

@TP-Link Yes, the main unit is solid green all the time. The satellite keeps blinking in red, not turn to green anymore. Just tried to reset the satellite unit, the problem persists My main modem is...

@TP-Link Submitted. There are around 20 clients connected to the Deco. Since the first post, the "issue unit" led is flashing red. But I am sure that the client in the bedroom is connected to that...

2 Deco M5 as AP mode connection as below: The LED on the 2 units are green but on the app it shows " Disconnected from other Decos"

Brand new M4 master unit get 200Mbps is maximum from ISP. But on the 2nd unit (wired to the master) is always cap at 100Mbps? if you need any information I will provide later.