Verify if your external hard drive is prepare to recognize Windows® Server operating systems and if it is any new firmware update for it.
It is compatible with the OS. There is not any firmware upgrades available for the drive. I have four of these drives all working with other Servers running the same OS version. They all work fine. When plugged into the NUC they do not. It is a problem, with the NUC. These drives are USB 3.0 drives and when I plug them into the NUC they show in the device manager as SCSI devices, which they are not.
Their drive icon in the File explorer continually flashes on and off. Disappearing then re-apperaing.
I have a Western Digital Portable 1TB USB 3.0 drive hooked up to it now and that works fine.
The problem might be some sort of compatibility issue, this seems to be an odd case but I would recommend checking the list of tested hardware.
As a workaround could you please Disable xHCI mode in the BIOS and test your external hard drive.
Devices tab>USB>xHCI Mode: Disabled; save and exit. I would like to test the compatibility of the USB 3.0 driver.
Let me know if your storage device is recognized by the NUC.