For devices which use the Odin protocol (Samsung devices only, I think), rebooting into the bootloader with adb reboot bootloader doesn't actually go into fastboot mode, but into the Odin download mode (which won't interact with fastboot). The command adb reboot fastboot, however, will go into a mode recognized by fastboot, so a one-line change in reboot_to_bootloader fixes this.
For devices which use the Odin protocol (Samsung devices only, I think), rebooting into the bootloader with
adb reboot bootloaderdoesn't actually go into fastboot mode, but into the Odin download mode (which won't interact withfastboot). The commandadb reboot fastboot, however, will go into a mode recognized by fastboot, so a one-line change inreboot_to_bootloaderfixes this.