S4 I9505 turns off on its own (probably network related)...
My wife's stock & unrooted S4 started to turn off when she returned for a vacation (she didn't use the network for 3 months; only wifi). From what she is saying and what I witnessed, it looks like an issue with the network : when she turned it on after a flight, it started to turn off itself after a minute. When she came home, I tested it and noticed the same issue. She wasn't getting any network signal however.
When I activated the wifi (don't think it's related but who knows), it started updating apps & everything and after a while, the network finally turned on and the phone stayed on for a full night. Phone calls & texting was working.
I thought it was settled but the phone turned off itself again after she got one of my message this morning; note that it's turning off without rebooting.
Is it a known issue ? Is there a fix or a test procedure I should go through ?
Phone is up to date.