Granted it isn't an issue with the UBS drive itself, try creating a bootable UBS drive with
Rufus. Its a quick and easy to use program to create bootable USB drives for utilities like Memtest or to flash your BIOS.
I had an issue with a iTB WD external USB HD that failed and gave me all types of problems during post and windows login. I had used USB 3.0 boost utility in AI Suite and I believe that may have contributed. Have you tried another UBS drive?