The debug ended with the following:
Running "chroot" ("/tmp/calamares-root-72i3rc21", "pacman", "-S", "libreoffice-still", "--noconfirm", "--config", "/opt/mhwd/pacman-mhwd.conf")
So I omitted libreoffice installation and made sure my bios/installer time was set right, resulting in the installer not hanging. Might want to check the installer libreoffice code…
Thanks for the debugging tip.