Bluetooth controls not working when screen is turned off

[Schnoinsch]

Plan

Premium

Country

Germany

Device

Oukitel K4000

Operating System

Android 5.1 (Stock)

My Question or Issue

Hello,
as long as my screen is turned on, i can skip tracks with the controls on my bluetooth earbuds, does not matter if screen is locked or unlocked. But as soon as the screen is turned off, the controls stop working.

Is this a known issue? Googling the problem leads to nothing, because the only problem that shows up, is the one where controls don´t work on lockscreen. 

But i got no issue there. Everything works as long the screen is turned on. As soon i turn it off, the controls stop working.

Greetings, Schnoinsch