Configure Autostart (for systemd)

You need to use a unit, rather than the VirtualBox built-in auto-start...

[Unit]
Description=${HOSTNAME} Virtual Machine
After=network-online.target

[Service]
Type=oneshot
RemainAfterExit=true
User=attie
Group=attie
ExecStart=/usr/bin/VBoxManage startvm ${VM_UUID} --type headless

[Install]
WantedBy=multi-user.target