Sometimes my auto brightness seems to go to sleep and stops making adjustments.
I'm careful not to cover the sensor.
If I go to settings and set brightness manually then turn auto back on it behaves for a day or two.
Yes. It even happened to me in the beginning where my auto brightness is completely stopped working. Even if I adjusted the brightness manually and then pressed "auto" it still didn't do anything. First I thought it died. But then, I shined a flashlight into the sensor and that brought back the auto adjust to life.
It still sometimes requires to touch the manual control, but if it completely stuck, the flashlight procedure will do the trick.
However, I just leave mine on manual control all the way down. It still gives me plenty of brightness in my room and this way at least it eats the least amount of battery.