I am having exactly the same problem.
Changing the scripts /usr/share/initramfs-tools/{hooks,scripts/local-top}/lvm and use PREREQ="mdadm" instead of PREREQ="md" indeed makes the system boot again.
I am having exactly the same problem.
Changing the scripts /usr/share/ initramfs- tools/{ hooks,scripts/ local-top} /lvm and use PREREQ="mdadm" instead of PREREQ="md" indeed makes the system boot again.