Thank you @friedl_1977! I took your advice and repeated the same process where I set up a new wifi connection, but to the hotspot on my mobile device - it connected without issue and breathed cyan and I was able to successfully query the variables via Particle Cloud.
I’ll try next week to do another test where I clear the credentials and try again. I’ll also try and do the same thing with my Argon (though I won’t be able to bypass authentication in that case). If that doesn’t do the trick, is there any known issue with respect to Photon and certain routers / configurations? Maybe the 20 vs. 40hz issue previously identified by @mterrill?
Edit: I’d forgotten that the Photon doesn’t work on 5ghz and I didn’t think to check with my customer regarding their wifi. But would it have successfully connected via the Particle app in the first place?
Edit #2: After more research, I think my issue is similar to this. I’m confirming with my customer, but I did only see one wifi SSID and I’m guessing / hoping it’s the issue where they have both 2.4 and 5ghz bands on the same SSID (per other threads).