Orbi RBS50 refuses to use wired backhaul instead of wireless backhaul

I suspect the ethernet connection.  A short ethernet patch cable worked, but the ethernet cable installed inside the walls failed?

Another quick test is to get a long ethernet patch cable (Amazon sells a 100ft. cable for under $20.

https://www.amazon.com/Mediabridge-Ethernet-Cable-100-Feet/dp/B003RCEAB8/ref=sr_1_4?dchild=1&keywords=ethernet+cable+100ft&qid=1612907369&sr=8-4 

Cable testers often verify that the correct wires are connected to each pin, but they do not necessarily verify that the connection meets the required performance test.  When my company rewired a building, we required the installers to provide a certification test on each cable.  The instrument used to do that costs thousands of dollars.  Often, the RJ45 connectors cause cable runs to fail.