Screen problem

[au5]

I set my Xperia XZs to sleep after 15secs of inactivity, but it seems to not follow it. Something is preventing it from going to sleep. If I don't press the power button and put it to sleep, the screen will just be lit for long (>15secs). 

Why is my phone like that? How to fix it? Any help would be appreciated. 

[MarlonUk1]

do you have the smart backligh enabled?

try to boot your device in safe mode,

[au5]

I do have the smart backlight enabled. But it's always been on since I first got the phone.
I tried booting it to safe mode, but nothing changed. 

[Ofense]

Since last Android Update Proximity sensor is going astray, always active...

that is even preventing you to cut your phone conversation, the screen sticking to black, preventing you from any action.

If you go in test section you will discover that proximity sensor vibrate whatever happens.