Hello,

New user here. Just migrated from ASCII to Beowulf doing a happyish dist-upgrade and stumbled upon this issue.

While the steps given by nemo76 (thanks for the hints!), there's a minor error in Head_on_a_Stick's diagnostic:

Echoing $prefix from the grub console, it says that the prefix points to /boot/efi/EFI/debian. Of course, debian doesn't exist. I found no way to connect the inconsistency, so I ended removing grub-efi-amd64-signed and now the system boots smoothly.

Thank you.