So the same issue was fixed in Arch Linux by explicitly mounting efivars inside initramfs: - https://bugs.archlinux.org/task/52768 - https://github.com/archlinux/mkinitcpio/commit/70511e5ccb7e2500213e04173a70c067a7c9aa35
Maybe the issue should be transferred to Debian's counterpart (initramfs-tools).
