Particle Photons are entering setup mode and never connecting to cloud again after a few hours of operation

I have 5 Photons out of which 3 worked fine till a few hours of operation. All of a sudden they failed one by one. Here is what I observed.

The Photon was working fine and then it launched its hotspot as if it was in setup mode. When I try to connect to Photon using the particle app it says, please put the photon in setup mode and try again. It was already in setup mode! The photon has been connected to the internet before. Somehow the WiFi credentials got erased. I don’t know why. When I restart the device it starts in setup mode every time. I even tried pressing the setup button for a while and setting it up. I was unable to do that.

Any suggestions on what’s causing this issue and how can I revive my Photons back?

Thank you