I cannot completely exclude that the incompatibility is between the USB drive and LB.
But I _can_ say that right after that particular USB drive with that particular Debian iso didn't work on my LB laptop, I took it out and put it into my T520 with BIOS and it booted. Also, I could boot Linux Mint 17.3 from a USB drive using the same USB port on my LB laptop, so it's not a USB port issue. I guess all I can say for sure is that this is a libreboot issue and it has something to do with either the Debian iso or with this particular USB drive.
