AR750S-EXT not working

A couple of years ago I purchased and AR750S-EXT Slate travel router. It works very well and is reliable. I’ve since tried several times to purchase a second AR750S-EXT router and none of them work consistently. I bought two used ones from eBay and had to return them. I recently purchased a brand new one from Amazon and that one does not work either.

In each case I would start them up and could not connect to them via WiFi - the SSID never shows up. I tried all of the reset procedures I could find, and I’d end up with one, two or three lights on (solid, not flashing) but no WiFi. I’d connect to the routers with an Ethernet cable but could not access the admin page. What is going on? The computers I’m using are both MacBook Pros. One is from 2014 the other is from 2020.