История изменений

Надо было выставить метку у файловой системы, вот здесь почитай: https://wiki.archlinux.org/index.php/USB_flash_installation_media

To boot either a label or an UUID to select the partition to boot from is required. By default the label ARCH_2017XX (with the appropriate release month) is used. Thus, the partition’s label has to be set accordingly, for example using gparted. Alternatively, you can change this behaviour by altering the lines ending by archisolabel=ARCH_2017XX in the file /mnt/usb/arch/boot/syslinux/archiso_sys.cfg (for BIOS boot), and in /mnt/usb/loader/entries/archiso-x86_64.conf (for UEFI boot). To use an UUID instead, replace those portions of lines with archisodevice=/dev/disk/by-uuid/YOUR-UUID. The UUID can be retrieved with blkid -o value -s UUID /dev/sdXn.

Либо указать UUID.

С другой стороны, даже по ссылке ходить не надо, в конфиге загрузчика всё указано:

INCLUDE boot/syslinux/archiso_head.cfg

LABEL arch64
TEXT HELP
Boot the Arch Linux (x86_64) live medium.
It allows you to install Arch Linux or perform system maintenance.
ENDTEXT
MENU LABEL Boot Arch Linux (x86_64)
LINUX boot/x86_64/vmlinuz
INITRD boot/intel_ucode.img,boot/x86_64/archiso.img
APPEND archisobasedir=arch archisolabel=ARCH_201707

INCLUDE boot/syslinux/archiso_tail.cfg

Надо было выставить метку у файловой системы, вот здесь почитай: https://wiki.archlinux.org/index.php/USB_flash_installation_media

To boot either a label or an UUID to select the partition to boot from is required. By default the label ARCH_2017XX (with the appropriate release month) is used. Thus, the partition’s label has to be set accordingly, for example using gparted. Alternatively, you can change this behaviour by altering the lines ending by archisolabel=ARCH_2017XX in the file /mnt/usb/arch/boot/syslinux/archiso_sys.cfg (for BIOS boot), and in /mnt/usb/loader/entries/archiso-x86_64.conf (for UEFI boot). To use an UUID instead, replace those portions of lines with archisodevice=/dev/disk/by-uuid/YOUR-UUID. The UUID can be retrieved with blkid -o value -s UUID /dev/sdXn.

Либо указать UUID.