@JCSMS yes, the downgrade to 1.8.0 solved the the problem.

Caption @ARGamingPK1 downgraded the devices to 1.8.0 and the issue has been resolved there is a bug on version 1.8.1

@David-TP log send FYI. I have chosen the below category from supper center "Encountering an Error When Adding a Deco" I have tried to add 2 different Deco M4R systems, both have same problem

Caption @David-TP I have bring the device closer to main deco and powered it without connecting the Ethernet cable. It is working as extender. but the wired thing devices show wired connected !!

@David-TP the mobile devices can't see the deco WiFi. Due to this issue, the SSID is not visible on for the devices on the coverage range of this device. Unfortunately I'm away from home for 2 days...

I have changed the subnet then rebooted the network but it didn’t work. Same behaviors