Laptop Suddenly Can't Find Extended Network on WN3000ROv3

On June 27, 2020 I successfully installed a WN3000RPv3 to extend the range from my landlord's wifi hub, in his basement, to my cottage, 35 feet away. I use a MacBook Pro, running Mac OS 10.15.5. I used to have to keep my laptop perched in a kitchen window to reach the wifi, and had a spotty connection even then. The wifi extender is in a bathroom window (a bit closer to the hub, with less interference between). For about a month it worked flawlessly. Then on July 30 I noticed my laptop was connected (spottily) to the main hub network, and not the extended network. I tried reconnecting to the extended network but my laptop "couldn't join..." I turned wifi off and on, shut down, restarted, and tried various ways to connect to the extended network. No dice. The extender's LEDs indicate a good signal to/from the main router, but the client light remains unlit. I've tried to get answers on Netgear's website, but link for Mac, Mac OS X or iOS, http://mywifiext.local, seems to be broken. Help! Why would it work for a month and then just stop working?