@Benwood118 Satellite Deco will deliver half of the speed on Main Deco, or even less. This is limitation of WiFi mesh technology. You have 400-450Mbps on Main Deco, that means you should expect up to...

@Zeick Your Deco mesh runs in its default Router mode. For that wiring to work, Deco mesh must run in Access Point mode. See Switching a Deco to Access Point (AP) Mode

@MrBeatnik You have very interesting case. You are correct, there is no setting to "persist" ethernet backhaul connection in one direction, or otherwise turn the WiFi backhaul connection option off....

@Benwood118 The issue with Ethernet cable has been resolved. If you can get 200Mbps on WiFi speed test, that means Ethernet cable runs at gigabit speed. Devices negotiate only discrete speed values...

@RolyPolyMacaron Deco should work through powerline and this powerline adapter model is what I usually recommend for people who want powerline link. TL-PA7017P has status lights. When upstairs...

@Zeick You said "other Decos, despite also being connected via cable" - but where do they connect, to the switch or to ISP router? From what you describe it appears they might be not wired as to be...