Photon going offline / online very quickly

I recently deployed six photons with the same firmware at the same location. Five are behaving correctly, but one is going through frequent offline-online cycles. Every thirty seconds to two minutes, the device goes offline and comes back online ( usually within the same second, sometimes up to three seconds ), according to the Dashboard. It seems like it might not be rebooting but just losing WiFi - they’re supposed to send me a message every hour, and they all do, but I still get an offline / online cycle every minute or so. All Photons are equidistant from the WiFi access point.

I managed to reboot it remotely using System.reset() and a few calls to delay(), but this problem persists. I don’t have access to the Photon for the next few weeks, so I can’t see what the LED is doing.

This looks similar to this thread : [Solved] Frequent photon offline-online-patch cycles
However, I don’t make any calls to Spark.connected().

Any thoughts much appreciated.

@Quentin Can you share what kind of code inside loop() ? Does it have delay calls? If yes, for how long? I experienced similar problem but now things have improved since moving to 4.5 firmware. You on 4.5 ?