Hello,
It's quite likely there there is a HW fault of this particular.
You can give it a try updating firmware of the dock - the latest (Dock_D6000_FW_Updater_
A04) can be found on a dedicated support page:
https://www.dell.com/support/home/uk...-d6000/drivers
Note: the fireware installer requires Windows PC to execute.
Regards
Szymon