I was able to build things properly before, but now consistently get these errors.
lb config noauto \
--distribution "stretch" \
--parent-distribution "stretch" \
--backports true \
--clean \
--ignore-system-defaults \
--mode "debian" \
--initsystem systemd \
--initramfs live-boot \
--compression lzip \
--debian-installer false \
--firmware-chroot false \
--apt-indices false \
--apt-recommends false \
--apt-secure false \
--memtest none \
--security true \
--linux-packages "linux-image linux-headers" \
--archive-areas "main contrib non-free"