Comment 4 for bug 1566387

Please provide the installer logs.

Option 1: boot the system (by manually mounting things from initramfs) and execute $ ubuntu-bug debian-installer, and either attach the generate apport report, or upload it to launchpad via offered means to open a new bug report.

Option 2: otherwise retrieve and attach /var/log/installer from such a system

This does look like a regression from btrfs zipl-installer enablement.