Sony Xperia XA dual sleep doesn't work

[Xxa]

I bought this phone 4 days ago.Well,actually Xperia xa is a one perfect device with smooth performance,good camera and fit for one hand but but after few days of use i realized that screen doesn't turn of automatically until i press the power button even if i set sleep after 15 seconds of inactivity.I tried through every settings but couldn't find any solution.Please help to solve this problem asap.Thank you

[Uliwooly]

Test it in > > > safe mode and report back. 

[Xxa]

It worked.A after i went through the safe. It automatically fixed when i back to normal mode..thank you for the tip

[Uliwooly]

It was a third party app acting up 

[Xxa]

Yea,I've read something like that recently but do you know how detect that app?

[Uliwooly]

Trial an derror I'm afraid