Had similar issue on osx and Nexus 5 (A6.0.1). I did get the authorization pop-up and confirmed it, despite that Android Studio nor any other IDE could connect to device.

Turned out my Nexus (rooted) was missing key files.

• Rebooted Android device into recovery
• Ran code pasted below
• Rebooted Android device, adb now identifies device

Push key from computer to Android device:

 cd ~/.android && adb push adbkey.pub /data/misc/adb/adb_keys

Solution came from here

Had similar issue on osx and Nexus 5 (A6.0.1). I did get the authorization pop-up and confirmed it, despite that Android Studio nor any other IDE could connect to device.

Turned out my Nexus (rooted) was missing key files.

• Rebooted Android device into recovery
• Ran code pasted below
• Rebooted Android device, adb now identifies device

Push key from computer to Android device:

 cd ~/.android && adb push adbkey.pub /data/misc/adb/adb_keys

Solution came from here