Dell USB 3.0 Dock USB Display Adapter Driver Disappears

 Latitude 6430u w/Dell USB 3.0 SS Dock. I have had several occasions of external monitor not coming on w/laptop lid closed. When this occurs, on opening laptop lid, found no Display Link Manager App symbol normally in task bar. On checking Device Manager under USB Display Adapter It shows 'unknown USB device'. First occasion I uninstalled the 'unknown USB device'. and rebooted, that however was no help. So next I disconnected the Dock from external power and the dock USB to laptop connector. Upon reconnecting, the system reinstalled the display link Driver,  and Dock once again correctly showed up in device manager and the external display comes on and works normally for a while (days/weeks), until once again it disappears.  Any thoughts or experience by others that might explain this random behavior of the Display adapter Driver? Update July 2016, Dock no longer works as USB display adapter for external monitor connection, all attempts to update/reinstall display link driver software has had no result, works only as a USB 3.0 hub.