Packer Ubuntu Server 20.04 prompting for install confirmation despite `autoinstall` specified in `boot_command`

I am setting up an unattended install for Ubuntu Server 20.04 with packer. However, despite my specifying autoinstall in the boot_command, the installer always asks me for confirmation (I need to manually type "yes" - in the middle of the screenshot):

This obviously defeats the concept of "unattended install", but I am not able to figure out what is the issue. I'm posting below two different boot_commands I'm using, and my full configuration at the end of the post.

Both boot commands produce a working installation, but both still ask for confirmation. Boot command 1:

boot_command = ["<enter><wait2><enter><wait><f6><esc><wait>", "autoinstall<wait2> ds=nocloud;", "<wait><enter>"]

Boot command 2:

      "boot_command": [
        "<enter><wait2><enter><wait><f6><esc><wait>",
        "linux /casper/vmlinuz autoinstall ds=nocloud;",
        "<wait><enter>",
        "initrd /casper/initrd",
        "<wait><enter>",
        "boot"
      ],

Full configuration: ./ubuntu2004.pkr.hcl:

source "virtualbox-iso" "autogenerated_1" {
  boot_command            = ["<enter><wait2><enter><wait><f6><esc><wait>", "autoinstall<wait2> ds=nocloud;", "<wait><enter>"]
  boot_wait               = "2s"
  cd_files                = ["./http/user-data", "./http/meta-data"]
  cd_label                = "cidata"
  disk_size               = 8192
  guest_additions_path    = "VBoxGuestAdditions_{{ .Version }}.iso"
  guest_os_type           = "Ubuntu_64"
  headless                = false
  http_directory          = "http"
  iso_checksum            = "sha256:f8e3086f3cea0fb3fefb29937ab5ed9d19e767079633960ccb50e76153effc98"
  iso_urls                = ["https://releases.ubuntu.com/focal/ubuntu-20.04.3-live-server-amd64.iso"]
  shutdown_command        = "echo 'ubuntu'|sudo -S shutdown -P now"
  ssh_agent_auth          = true
  ssh_handshake_attempts  = "200"
  ssh_private_key_file    = "/home/asdf/.ssh/virtual_id_ed25519"
  ssh_username            = "vagrant"
  ssh_wait_timeout        = "10000s"
  vboxmanage              = [["modifyvm", "{{ .Name }}", "--memory", "1024"], ["modifyvm", "{{ .Name }}", "--cpus", "1"]]
  virtualbox_version_file = ".vbox_version"
  vm_name                 = "packer-ubuntu-20.04-amd64"
}

build {
  sources = ["source.virtualbox-iso.autogenerated_1"]

  provisioner "shell" {
    scripts = ["scripts/init.sh"]
  }

  provisioner "shell" {
    scripts = ["scripts/cleanup.sh"]
  }

  post-processor "vagrant" {
    compression_level = "8"
    output            = "ubuntu-20.04-test.box"
  }
}

./http/user-data:

#cloud-config
autoinstall:
  version: 1
  locale: en_US
  keyboard:
    layout: en
    variant: us
  network:
    network:
      version: 2
      ethernets:
        enp0s3:
          dhcp4: true
  storage:
    layout:
      name: lvm
  ssh:
    install-server: yes
  user-data:
    users:
      - name: vagrant
        ssh_authorized_keys:
          - ssh-ed25519 REDACTED
        sudo: ALL=(ALL) NOPASSWD:ALL
        groups: [adm, sudo]
        lock_passwd: true
        shell: /bin/bash
  packages:
    - openssh-server
    - build-essential
  late-commands:
    - echo 'vagrant ALL=(ALL) NOPASSWD:ALL' > /target/etc/sudoers.d/vagrant