So testing with Fedora's boot/efi/EFI/fedora/grubx64.efi in place of the Ubuntu version solves the problem.
So it is indeed the situation that you describe in comment #15
So testing with Fedora's boot/efi/ EFI/fedora/ grubx64. efi in place of the Ubuntu version solves the problem.
So it is indeed the situation that you describe in comment #15