GS308EPP for Mesh Ethernet Backhaul with Deco X50 PoE

Try a non managed switch in between the router unit and the satellites. 

Contact TP-Link for help and information regarding there product as well. There maybe specific configurations needed. 

Orbi MESH uses this kind of configuration with a switch in between:

https://kb.netgear.com/000051205/What-is-Ethernet-backhaul-and-how-do-I-set-it-up-on-my-Orbi-WiFi-System 📡 ‌‌🛰️