Weird Photon boot loop

My Photon weather station was working fine for over a year. Now lately it has developed, all on its own, a weird problem. When I apply power, it does blinking green -> quick flashing cyan -> steady cyan for about a second -> a single bright white flash -> dim white (gray?) -> repeat forever. The whole cycle takes about five seconds.

Holding Setup for three seconds to put it in Listening Mode does not. It goes to flashing yellow. So taking a clue from that, particle flash --usb tinker did finally work, though it took over a minute.

It does this even near my router, so signal strength is not the issue. I’ve never seen this before. What could this be?

Well nothing heard so I’ve opened a support ticket.