@Hisham_A you can check if you main Deco was connected and 1000mbps not 100mbps on Router, i think auto-negotiation fail with router and limit your connection to 100mpbs to main deco. Due this you...

@Hisham_A You make speed test via Ethernet? Try this, put ethernet cable on slave deco and make it, this is a real backhaul speed between slave and other deco. Remeber wifi clients can be slow than...

@Hisham_A You can use powerline to avoid WifiBackhaul down speed. Or ethernet from main deco. 8 ports switch linked to main deco and all others deco's. i have 300mpbs fiber here and got 300mbps in...

@rmnayve Here you got 1.4.2 version: https://community.tp-link.com/en/home/forum/topic/187114 And update via web gui.

@Janingo No, you can't read at Deco App, but have some app to do this. Windows/Mac: https://www.netspotapp.com/ Mac: https://www.adriangranados.com/ (Wifi Explorer) Wifi Explorer o Mac, but rememer...

@Hisham_A yes, any unit connect at any unit in range but for best performace with wifi backhaul use any software for meansure SNR signal between units, if you get plus 24db of SNR wifi backhaul works...