The problem using manjaro as system to build an arch-based distro is that some (or most) of the core packages are renamed, since manjaro compile and pack with their own specifications and use different names. This require you to adapt the necessary names at packages_x86_64 file
This error you got seems to be cause by a different kernel name on manjaro (or even the way the iso is set to boot); AFAIK manjaro uses grub to boot the iso, while arch uses syslinux.
So using a VM as @FredBezies said is a good alternative, or having a fake system root inside your manjaro system (VM is easier and has the live environment to play with OOTB, so it’s better)
caused by the issue with fonts for terminal and mousepad + to get asian fonts working configs are not working completely at the moment… also due to changes inside installer to get network install working there are some major changes at the moment we are working on, we do setup configs for livesession with this:
But very nice to see our ISO is booting fine and is stable as we do like it