$ buildiso -p base
/snip/
==> Creating xz-compressed initcpio image: /boot/initramfs.img
bsdtar: Failed to set default locale
bsdtar: Failed to set default locale
==> Image generation successful
--> overlayfs umount: [/var/lib/artools/buildiso/base/artix/bootfs]
==> Done [/iso/boot]
==> Prepare [/iso/boot/grub]
cp: cannot stat '/var/lib/artools/buildiso/base/artix/rootfs/usr/share/grub/cfg/*.cfg': No such file or directory
==> ERROR: A failure occurred in make_grub().
Aborting...
Complete log
https://pastebin.com/tmmAmdhA
Yeah I noticed this error started happening to me as well all of a sudden. I'll try to remember to bug Artoo about it.
There has been a change in the profiles and the packages, not yet merged in master. Put artix-grub-live and artix-grub-theme in Packages-Live and artix-grub-theme in Packages-Root. Or use the refactor branch.