Searched but didn't see matching post. I have deco x3600 with two satellite nodes. My house is only 1,200 sq feet and the satellites are strictly to get signal to my outside devices (Doorbell in front, camera in the back.) There's no obstacles other than a stairway between the satellites and main. To my knowledge, system is tri-band, with a band dedicated to backhaul.
Using my iPhone 11, my main deco consistently puts out 350MBps everywhere in my house except outside. However, when I allow my iPhone to connect to a satellite - even one that's 5 feet away - it gets a max of 10 MBps, and its speed outdoors is around 5, despite being right by a window rather than solid wall.
Why would the nodes be SO MUCH SLOWER than the main, when it's a tiny house with no interior obstacles? It's tri-band with a dedicated band for wireless backhaul, so I'd expect only minor speed loss. Is there some setting that's possibly killing the connection between the satellites and main? I'm not kidding when I say that one is 20 feet away with no obstacles (not even a door), while the other is 10 feet away (literally immediately downstairs from the main.)