Have you tried your Seagate* 3.0 drive (8TB, model STDT8000100) on another computer to find out if it is an issue isolated to the unit?
Please confirm your Intel® NUC5i5RYH drivers are installed and up to date in the Windows* Control Panel. You may download the latest drivers by either running the Intel® Driver Update Utility or manually downloading specific drivers from Intel® Download Center
You may also try reviewing your current BIOS version on your Intel® NUC5i5RYH the latest version available is 0350 which could be downloaded from here Intel® Download Center
Please let us know about the outcome.
*Other names and brands may be claimed as the property of others.