@FrannyK 16 meters from Main Deco is too far for Satellite Deco. In Deco app, check what does it tell about quality of signal. This will be in "Show List" page, something like this: Also, open...

@NAlex This is supported. It is first network diagram in Q2 of TP-Link FAQ document: General questions about Ethernet Backhaul feature on your Deco

@FrogXL I would recommend running Deco mesh in Access Point mode. In that mode, you can wire Deco units any way you want. Wire each Deco, including Main Deco, to the switch: If you have free ports on...

@nkw1985 I would suggest switching Deco WAN link back to gigabit port. Not in this Deco model, but 2.5 GBps port caused some issues. Especially, if your modem has gigabit port, you would not want to...

@nkw1985 That looks very much like Main Deco negotiating 100Mbps over Ethernet link to the ONT modem. When you reboot Main Deco, it'll briefly renegotiate gigabit speed but can't keep it due to...

@NetStream 1. Where is ISP router/modem on that floor plan? 2. Do you plan to have Satellite Deco(s) connected with Ethernet cables to Main Deco, or using WiFi? 3. What is firmware version of Deco...