1) type 'normal' at the prompt; we should make sure that the grub.cfg config is read file and the menu can show in this case.
2) Are you installing with hwe-xenial kernel? If not, could you please try this?
3) If none of this works; we'll get you a debug version of grub2 or just grub-install for testing with some extra logging, so we can see what happens when it attempts to write that last line to grub.cfg in the EFI path.
Could you please try a few things?
1) type 'normal' at the prompt; we should make sure that the grub.cfg config is read file and the menu can show in this case.
2) Are you installing with hwe-xenial kernel? If not, could you please try this?
3) If none of this works; we'll get you a debug version of grub2 or just grub-install for testing with some extra logging, so we can see what happens when it attempts to write that last line to grub.cfg in the EFI path.