Hello,
Thank you for reaching out to us here on the forum.
Based on your issue description I would recommend updating your Firmware version in your D6000.
To do it you will need to download FW update
from here and plug in your D6000 to a Windows machine as the update can be only performed on Windows OS.
Please download the update and plug in the D6000 to your Windows machine (without USB devices/monitors plugged in to the D6000). Then run the update and follow steps visible on the screen.
Afterwards, please plug in the D6000 back into the Macbook and verify if the issue still persists.
In case of any questions, please let me know.
Thank you for your further feedback!
Kind regards,
Jakub