My Nexus 7 2013 has updated with OTA update to Android 5.0.1.
The notification bar has changed. Now when I change brightness, there is no button for auto-adjustment. It currently looks like this:
In settings, I can find Adaptive brightness settings - optimize brightness level for available light. However this does not work as expected. It just seems I have two different brightness settings. If I turn it on and set manually via notification bar to maximum, it is maximum, although the settings is ON. Then I turn it off and set it to maximum and it lets me do it too. When it is turned on, the brightness is just slightly darker than the turned OFF mode. However, it is always exactly as I set it with this small offset. It does not correspond to the external light.
It seems like it is a bug, but I can't tell. Do you experience the same with your Nexus 7 2013? Is the "auto" button missing in all lollipops? Does it mean that when you want to go to auto-brightness mode you have to enter settings and brightness via more like 5 clicks? (two swipe downs, settings, brightness, turn on)