Cant't increase headphone volume above certain threshold

Hi there,
a few weeks ago, my DTEK50 has started to show a strange behaviour. When headphones are connected I cannot increase the volume above the "safe Limit" .
Normally a message would show up to remind me of the danger of high volumes. This message is now completely missing. So I'm stuck with a mediocre volume weile using headphones.
Trying to increase the volume further using the system settings does not work.Different headphones make no difference.
Without headphones everyhting is working fine.
Im on the following software:
Android 6.0.1. Security patch Septemter Build A0571

Thanks in advance

1) Go to settings, Apps
2) Click the settings wheel in the top right corner
3) At the next screen, click Draw Over Other Apps
4) Click the three dots in the top right corner and click Show System
5) Then scroll down the app list and find SystemUi and toggle to Yes

Thank you very much!
I thought it was an issue with this display overlay stuff but couldn't find it.
Thumbs up!

Thank you very much!
I thought it was an issue with this display overlay stuff but couldn't find it.
Thumbs up!