Comment 6 for bug 1747329

Extracting tools can be affected by this "gfxboot.c32: not a COM32R image" bug. It is a problem of the tool to create the USB boot drive, and should be fixed by the developer of that particular tool.

-o-

Cloning tools are not affected by this bug. You can use Ubuntu's Startup Disk Creator alias usb-creator-gtk in Ubuntu 16.04 LTS and newer versions, or Disks alias gnome-disks, which both are GUI tools with a final checkpoint and they are packaged with Lubuntu. You can also use mkusb, which can be installed from a PPA. mkusb can clone, but also extract and create a persistent live drive.

As mentioned by Steve Langasek, you can also use dd, but it is risky, because it does what you tell it to do without questions and many people have overwritten valuable data after a minor typing error or some other (minor?) mistake.