I have 2 new Deco X90s and 2 new Deco W7200s  connected via Ethernet in my house. Three devices are all connected via Ethernet to the main router via a switch. Ethernet Backhaul is working on the two W7200's. But the second X90 is connecting via WiFi instead of the Ethernet cable it is attached to.

The set up is as follows:

Cable Modem via Ethernet cable directly to X90 Main Router, which is connected via Ethernet cable directly to TP-link 8 hub switch. Three Ethernet cables from switch to ports that connect to X90 Satellite, W7200 Satellite #1, and W7200 Satellite #2 in other parts of the house. The ports are all working and I've checked the cords throughout; they are okay. But the closest one to the main router, the X90 is connecting via WiFi backhaul instead of Ethernet

Is there a limit to how many satellites can be attached to the main router by Ethernet Backhaul? I couldn't figure that out from the documentation. (Maybe I'm missing something?) I would like to add one more to a remote part of my property via Ethernet as well, but if there is a limit to the number of satellites in a system, I'm not sure how to configure this.

Should I run them all on WiFi Backhaul instead of Ethernet? Or via Access Point somehow? Or am I missing something in the current configuration? The TP-link switch is TL-SG108E. All of the software is up-to-date.

Thanks.