Since the A11 update I have an intermittent problem with the display going black when a call comes in. I haven't been able to establish a firm pattern or situation when this happens, but I have a feeling that it is just when I'm using the phone with some other app. A call comes in, display goes black, the ring sound is active and I'm not able even to get the buttons visible at the bottom row. If I press the on/off, that cuts the call and after a moment the phone goes back to normal. 

In general, I am frustrated with Android as there can be so many different ways the phone  behaves with an incoming call. Most often you swipe up to answer, sometimes you get buttons at the top, sometimes an app can hide all this - and now the screen goes black.

I know that I might get crucified for this, but I do miss the Windows phone. Maybe there weren't all apps available, but it was a solid business phone that integrated well to the business infra and was totally predictable. Android is a toy. Sigh...