I have the same issue with the latest alternative bionic image (clonezilla-live-20180812-bionic-amd64.iso) and the same fix works (adding "set root=hd0,msdos1")
I confused UUIDs with Disk IDs, actually the Disk ID changes because of cloning the machine and the Disk ID would need to be rewritten.
Rewriting device UUIDs in /etc/default/grub and /etc/default/grub_installdevice