Welcome to Android Central! Is there anything magnetic coming near the device? Many devices these days have magnetic smartcover sensors that will detect the weak magnet in a case with a screen cover, such that when the cover is closed, the sensor detects it, and turns off the screen. When the cover is lifted, the sensor detects that the magnet is removed, and activates the screen again. If you have some magnet that is coming near this sensor, it could shut off the screen.