Unfortunately I've tried just about everything including a different physical location and therefore different AP and internet connection, still the same symptom. Also saw elsewhere in the forum
"Alas, it is not enough to use non-blocking delays with millis(). I use it everywhere, but despite that I was always loosing cloud connectivity after a while with several such non-blocking functions. After loosing cloud connectivity the Photon did not reconnect by itself and I had to reset it."
Seems like others have this issue as well even of the code in loop does not have a delay ?