Brightness level stuck at minimum after upgrading to Android 5.1.1

I have Sony Xperia Z (C6603, 10.7.A.0.222) and the brightness level is stuck at minimum after update to 5.1.1. I have tried: - sensor test - light sensor is OK. - set brightness via ADB (settings put system screen_brightness 200) - didn't work. - using brightness control apps (like LUX for example) - didn't work. Using stock ROM without root, any apps or functions that could set brightness to low for saving battery are either uninstalled or turned off? Any suggestions?