Layout Field type != Layout Field type?

I’ve been trying to replicate a behaviour of the Starterkit on the plain kit, however when I do so it emerges that this causes an error.

I’ve created a page template called ‘Block Page’.

title: BlockPage

status:
  draft: true
  listed: true

options:
  changeSlug: true
  delete: true

tabs:
  content:
    icon: text
    label: Content
    fields:
      layout:
        label: Layout
        type: layout
        layouts:
        - "1/1"
        - "1/2, 1/2"
        - "1/3, 1/3, 1/3"
        - "1/1, 1/2, 1/2"
        - "1/1, 1/3, 1/3, 1/3"
        - "1/1, 1/3, 1/3, 1/3, 1/3, 1/3, 1/3"
        - "2/3, 1/3"
        - "1/3, 2/3"
        - "1/4, 1/4, 1/4, 1/4"
        - "1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4"

I’ve based it off the ‘About us’ blueprint from the starterkit.

title: About us

icon: ☎️

status:
  draft: true
  listed: true

options:
  changeSlug: false
  delete: false
tabs:
  content:
    icon: text
    label: Content
    fields:
      layout:
        label: Page Content
        type: layout
        layouts:
        - "1/1"
        - "1/2, 1/2"
        - "1/3, 1/3, 1/3"
        - "1/1, 1/2, 1/2"
        - "1/1, 1/3, 1/3, 1/3"
        - "1/1, 1/3, 1/3, 1/3, 1/3, 1/3, 1/3"
        - "2/3, 1/3"
        - "1/3, 2/3"
        - "1/4, 1/4, 1/4, 1/4"
        - "1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4, 1/4"
  contact:
    icon: map
    label: Contact
    columns:
    - width: 1/2
      fields:
        address:
          label: Address
          type: writer
          inline: true
        email:
          label: Email
          type: email
        phone:
          label: Phone
          type: tel
    - width: 1/2
      fields:
        social:
          label: On the web
          type: structure
          columns:
            platform: true
          fields:
            platform:
              label: Platform
              type: text
              width: 1/2
            url:
              label: URL
              type: url
              width: 1/2

However, within my plain kit set-up, I’m getting an error that I cannot fully resolve, nor provide a stack trace for.

I’ve tried to google/ai chatbot my way through it, but nothing helped so far.