I have run into a problem related to this when Debian Stretch made a system upgrade. A fresh install of it or (l)ubuntu did not remedy.
Symptom
After a system installation or a system upgrade grub does not get loaded. After the manufacturer splash screen a message beginning with "System BootOrder not found." appears for a second or two and the computer reboots.Cause
The wrong file is at EFI/Boot/bootx64.efiSolution
Copy EFI/<your operating system>/grubx64.efi to afore mentioned lockation likesudo mount /dev/sda1 /mntsudo cp /mnt/EFI/ubuntu/grubx64.efi /mnt/EFI/Boot/bootx64.efi
