Comment 25 for bug 1437024

Actually, nevermind that. The files would not be signed correctly to work with Secure Boot (at least, not without more fiddling).

Please use http://archive.ubuntu.com/ubuntu/dists/artful/main/uefi/grub2-amd64/2.02~beta3-4ubuntu6/grubnetx64.efi.signed , using that file from artful (to replace your grubx64.efi) should be sufficient to test. It already includes the fix.