You can build these isos if you have the right version of Archiso.

Archiso is a package supplied by Arch Linux that is recently undergoing some major changes.

You can follow up the versions via this link.

https://www.archlinux.org/packages/extra/any/archiso/

We are now using this version


archiso-version=50-1.1


sudo pacman -Q archiso and you will know your version


Downgrade to this version via a command in the terminal if you have a higher version.

downgrade archiso

and choose the right version. 

Add it to the ignore list of pacman.


If you have a lower version then update your system. Check to see if archiso is not added to 
your /etc/pacman.conf in the list of ignores. Delete it if it is in there. Then update.