When upgrading the Linux kernel I encountered an issue where the new kernel was not correctly identifying and decrypting my volume. Fortunatley I was able to access the system using an older kernel.
It seems that a critical package had been removed, as redundant.
apt install cryptsetup-initramfsAdd CRYPTSETUP=Y to /etc/cryptsetup-initramfs/conf-hook
update-initramfs -u -k <problematic kernel>