Ubuntu 18.04 installation fails to install grub on /dev/sda

[Bear Baker]

I have an old laptop (Samsung RV511, from around 2011), tried to install a custom Ubuntu 18.04 installation (built using Cubic and uploaded successfully in a VM).

Mid-installation, I received an error, something along the lines of:
Grub installer failed to install Grub on /dev/sda

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.14
ProcVersionSignature: Ubuntu 5.3.0-40.32~18.04.1-generic 5.3.18
Uname: Linux 5.3.0-40-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.11
Architecture: amd64
CasperVersion: 1.394.3
CurrentDesktop: ubuntu:GNOME
Date: Sat Jun 6 17:12:55 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper only-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 18.04.4 2020.03.13 LTS am "Aviad's Custom BASIC Ubuntu Beaver" (20200313)
ProcEnviron:
 LANGUAGE=en_IL
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IL
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)