I used ADB the first time since I have updated my FP OpenOS to Android 6.
Thus I noticed that the ADB connect is not working properly.
A similar behaviour was formerly described in Adb does not work after update to 6.0 which is unfortunately closed 6 days ago (with no way to reopen it). @avonrepus already mentioned the possibility of an error.
So I am opening this new thread with detailed Information to the problem:
The workaround of @avonrepus switching “Developer Options”/“Select USB Configuration” to “Charging” successes only for one time. If I reconnect the usb cable than this option switched back to “MTP” once again.
Additionally after automatically switching back to “MTP” in Developer Options the next status in connection popup after plug in usb is “Charging”?! Very buggy.
Also the workaround of @paulakreuzer in the earlier and also closed thread ADB on FP2? Solved: Uncheck all boxes in USB connection popup is no longer possible because there is no chance to uncheck all boxes in the notification window.
The best solution I found is to select MIDI in the popup notification window after plug in usb cable.
Although I have found a workaround I think that should become an issue in the bugtracker.