I'm pretty sure that the auto brightness thing is based off a sensor at the front, which if being used in certain conditions and ways can be affected by your finger placement or shadows created by your head/hands/whatever.
Whenever it happens to me, seemingly at random, it is one of the above usually causing the fluctuations in screen brightness.
Whenever it happens to me, seemingly at random, it is one of the above usually causing the fluctuations in screen brightness.
