Since I upgraded to 8.1 my ambient screen doesn't work properly, black screen on calls and so on. I'm pretty sure it's some change with the proximity sensor. i used some apps to test the sensor and when I clean my screen really hard everything works fine (shows "far" in the test app) but when i just wave without touching the screen, it goes to "near" and doesn't recover until i wipe the screen again ( wtf?). I can't really use the phone like this. I am in contact with Google support but they give the generic suggestions like restart the phone etc.
Everything worked fine under 8.0. i actually went ahead and flashed 8.0 back on and it works properly. it seems like they increased the sensors aggressiveness in 8.1.
For most people the problem gets resolved by taking off the screen protector but I don't have one applied. neither are there any scratches on the display. Maybe my sensor is flawed in some way :/
I also tried the turning on /off adaptive brightness trick, to which there is a thread somewhere.
maybe you guys can share your experiences or fixes,
Thanks and Liebe Grüße from Germany !