Thank you for all this information.
I would like to verify just some information:
- Is the NUC running the latest BIOS? If not, try updating it here:
- Just to confirm, what Linux version are you trying to install?
I was on FY0040 (2014-Sep-23). Have just updated to FY0041 (2014-Oct-29). Nothing has changed.
I am running Slackware 14.1. The partition was created with gdisk. The EFI partition was formatted with mkfs.vfat and efi file created from GRUB 2 grub-install to /EFI/slackware-14.1/grubx64.efi. I copied that to /EFI/BOOT/bootx64.efi.
Everything works fine if I boot it with USB UEFI grub setting the root /dev/sda3.