I had this also. I made a warranty return. Now the second NUC works.
Hello Geoninja, I absolutely agree with Kari-s since the replacement NUC is working without problems.
I would recommend you to check if you are using the latest USB 3.0 drivers
If you continue having issues please contact our Warranty department so they can help you. http://www.intel.com/p/en_US/support/contactsupport