grub iso usb flash config snippet

gistfile1.txt

menuentry 'Debian 8.5.0 amd64 CD 1 XFCE' {
        set isofile='/iso/debian/debian-9.3.0-amd64-xfce-CD-1.iso'
        set initrdfile='/iso/debian/initrd.gz'
        loopback loop $isofile
        linux (loop)/install.amd/vmlinuz iso-scan/ask_second_pass=true
        initrd $initrdfile
}

menuentry 'Gentoo live DVD amd64-hardened' {
        set isofile='/iso/gentoo/livedvd-amd64-hardened-nomultilib-20170118.iso'
        loopback loop $isofile
        linux (loop)/isolinux/gentoo iso-scan/ask_second_pass=true
        initrd (loop)/isolinux/gentoo.xz
}

first one boots, second one does not

gentoo kernel loads and then stalls, don't see unpacking of initrd