One more question. I have recognized that several ZFS packages have been updated (see history.log attached above; e.g. libzfs2:amd64 (0.6.5.8-pve13~bpo80, 0.6.5.8-pve14~bpo80) and then the problems started. But Grub is still from November 30, 2016. Might this be the reason for Grub not...