A problem I have encountered every time I use a USB drive as a Startup Disk, is that their block size get changed, and even gparted reports that it can’t fix the that. The following command will fix that.

sudo dd if=/dev/zero of=/dev/sdX bs=2048 count=32

Be sure to replace sdX with the drive identified (Eg: sda, sdb, sdc, etc.).

And then format the disk with your tool of choice (Eg: gparted, or gnome-disks.)