Reinstall the GRUB boot loader to your Ubuntu installation in EFI mode this way (From live CD)

grub_efi_loader.sh

sudo mount /dev/sdXXX /mnt
sudo mount /dev/sdXX /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sdX
update-grub

# Note : sdX = disk | sdXX = efi partition | sdXXX = system partition

# 'Fixed' by replacing /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi with /boot/efi/EFI/arch/grubx64.efi

# Resources
# https://community.acer.com/en/discussion/471754/acer-aspire-es-15-es1-533-c3uw-legacy-bios-missing
# https://askubuntu.com/questions/862946/unable-to-install-ubuntu-on-acer-aspire-es1-533