My S6 is about 1.5 years old. Since about 3 days ago (Friday, 4/28/17), I've started having this problem.
The phone randomly makes a beep noise, and then turns black. A white "x" appears on the bottom of the screen. Then, the black screen disappears and it displays whatever I was looking at prior to the black screen's appearance.
I've noticed that every time the black screen with the white "x" appears and disappears, my phone can't charge afterwards. I've tested two cables, plugged the phone directly into a wall socket, and tried two different adapters. I've made sure both the cables and both the adapters work by testing them with another phone.
Forums show that other people had similar problems in the past. However, their black screen and white "x" actually stays on the screen without disappearing. And, they don't report any problems with charging. The black screen and white "x" seems to be associated with some Samsung Gear VR app though ...
Using the reboot trick (power button + volume down), I am *sometimes* able to get the phone to charge after the reboot. Other times it'll reboot but still be unable to charge.
Alternatively, I tried shutting the phone down normally (hold power button, select red "power off" button). Same thing happens; sometimes it'll work when I start up the phone again, sometimes it won't.
I've also plugged the phone into a portable charger and the charger would light up, as it normally would when it's charging a phone. Despite the charger lighting up, my phone wouldn't actually be charging.
I've already tried factory reset. I've also tried wiping the cache from recovery mode. No good; problem still persists.
I'm out of ideas.
Any help is appreciated.