There are Hardware Tests for all of these features. Can you run them and let us know if the phone's operating as it should as far as the hardware's concerned?
To access Hardware Tests, go to the Phone app > Dial *#0*#
Auto Rotate: Select SENSOR in the Hardware Test menu > Tap IMAGE TEST under Accelerometer Sensor. An image of a dog will then appear. If it's working as it should, rotating your phone will rotate the image.
Iris Scanner: Within the Hardware Test menu, select IRIS CAMERA TEST and follow the steps outlined on screen.
Auto Brightness: Test this when you're in a well lit environemnt. Select SENSOR in the Hardware Test menu > Tap LIGHT SENSOR. If it's operating correctly, moving your hand over the sensor at the top of the screen will change the values on screen from Level 2/3 to Level 1.
If your phone fails any of these tests, head to a Service Centre to arrange a repair.