Update: Developers at Fairphone “rejected” the issue, there will not be a fix by Fairphone as long as the Fairphone is running android 6. The reason for the rejection is, that this would be a “generic” and rare Bug directly in the Android codebase that affects other devices but never got fixed by Google. Rick from Fairphone supplied thus link:
https://support.google.com/nexus/forum/AAAANseOu18LX962Qnx2Do/?hl=en
Please use the workaround above, which worked for me.