I also have the same issue with my Photon. I received it less than 2 weeks ago and setup was working fine for some time after the OTA update.
@JeffL Does your Photon stay/go back into Listening Mode after passing the credentials? I tried connecting through the App, Particle-CLI (WIndows), and through a Serial connection (Putty), and they seem to pass the credentials to the Photon successfully. However, after the Photon receives the credentials, the LED turns solid green (not blinking/breathing) for about 2 seconds, and then goes back to blinking blue as if it was back in Listening Mode. It stays there until I hit the Reset button, and then successfully connects to the cloud.
I also tried following the instructions for WiFi Network Reset (https://docs.particle.io/guide/getting-started/modes/photon/#wi-fi-network-reset) but that doesn’t change the results.