@Cybersmythe Are you managing in Standalone mode or Controller mode? Can you provide the firmware version that you upgraded to? 
Lastly, if you plug a laptop directly into the LAN port on the client AP, are you able to ping the main AP? 

  @NeilR_M Standalone mode.  If I plug the cable from the PoE injector into a laptop, I don't get link so there's no IP address.

The version on the client reports "1.1.3 Build 20250805 Rel. 76570(5553)"

  @Cybersmythe If you go to the IP of the Main AP and log in, then go to Bridge Network > Bridge APs List > Add Client-AP, after scanning, does the Client-AP appear in the list? 

  @NeilR_M I don't need to do all that.  When I go to the Bridge Network page, it shows the both of the units on the bridge network, and it's already listed in the Bridge APs list.  I can also do the same after attaching to the Client AP directly.

  @Cybersmythe So if you can access the Client AP's page, can you try reverting to the previous firmware version and seeing if it resolves the issue? 

  @NeilR_M I don't think a downgrade is possible.  I didn't write down what the old firmware version was, but even if I did it says "rolling back to any of the previous versions are forbidden".  I would attempt it, but I don't know where to download it from, or if it would be at all likely to work.  My experience programming similar devices suggests that there are usually really good reasons to prevent downgrades.

At this point, I'm pretty much resigned to climbing back up on the roof and bringing the device down so that I can try things like different cables, non-PoE  with connections on different ports and such to see what's up.

  @Cybersmythe our support team can provide a firmware for downgrade; please reach out to them here: https://support.omadanetworks.com/