@WindowsNT_Cork Do not enable Guest Network - and if you already did, then disable it back. Having Guest Network enabled will not do any good: these mysterious devices are connected to your Main...

@Maurits_1971 As I thought: firmware 1.2. Also, your M9 Plus is hardware version 2. Follow this document to upgrade your M9 Plus: How to Update the Firmware of Deco Try Method 3 and if that does not...

@Maurits_1971 I saw this happening when Deco M9 Plus has very old firmware, version 1.2.*. I can't tell if all devices connected to Main Deco is just a reporting issue or they indeed only connect to...

@cjferoussis I am not from TP-Link, so I would not know, but even TP-Link Support that checks this forum is not privy to that info. I can see you have M4(R) hardware V2 and S4 hardware V2. You may be...

@cjferoussis This feature, disabling Smart DHCP, will become available in firmware 1.6. That firmware may or may not be released for X20 V1. Can you share Update Deco screenshot from your Deco app,...

@Paul________C This is what you will need to take into consideration when deciding Router vs. Access Point mode: 1. Do you have ISP provided router/gateway, or they only provide you with modem which...