I have a "chain-star" style of connection for my Decos all through Ethernet. 
Internet -> Living Room Deco (Main) -> Switch in Study Room -> Study Room Deco -> Main Room Deco.

The problem I'm having is I literally have a FireStick besides the Main Room Deco, but it's connecting to the Study Room Deco which is in the next room. Same with a Google Home mini in the main room connecting to the Study Room Deco.

Initially my original problem was that I was connecting my Decos wirelessly and the main bedroom Deco was connecting to the living room Deco which is 2 rooms away, instead of the living room Deco. This made me so angry and I searched the forums and everyone is having this problem and Tp-Links's only answer is their developers have this as part of their to-do list without an ETA or certainty a "Select Which Deco to connect to feature" will be developed. So I solved this by hard wiring everything through Ethernet/switch and now I have the same speed on all three Decos, but guess what the Main Room Deco is worthless because no device is connecting to it even though they are 1 or 5 feet away from the Deco.

This is absurd and cheap product development from TP-Link and hope somebody raises this as false advertising against TP-Link, who claim  the Deco x20 will properly resolve the connection to the best/nearest Deco.

Hope someone has found a fix to this problem, because I for one have tried many options and I think my last resort is to remove the Study Deco, which would be absurd because I purchased the 3 Deco set for a reason.