Filepicker not working inside a list with elements fieldtype

My filepicker dropdown fields aren’t being populated with the list of page media as expected.
These troublesome filepickers are inside a list containing the elements field type.

Here’s a snippet from my page blueprint:

header.content_blocks:
  type: list
  style: vertical

  fields:

    .type:
      type: elements
      label: "Content Type"
      size: small
      default: image
      options:
          image: Image
          ...
      fields:

        image:
          type: element
          fields:
            .file:
              label: Select Image from Media
              type: filepicker
              folder: self@
              preview_images: true
        ...

I’ve noticed that the documentation for elements only includes text fields.
Is this a known limitation with the element field type?

Further info:

  • The filepicker dropdown is empty when I select it.
  • I get a “Not Found” error flash up when loading the page in admin.
  • Other filepicker fields work correctly outside of the list (ie: header.image works; the list of page media is shown when I click on the dropdown).
    – Text fields inside the elements field are working as expected.
  • If I move the .file to the root level (ie: header.file) OR outside of the elements field (ie: header.content_blocks.file) it works as expected. So the blueprint seems to be valid, it just doesn’t work when it’s inside the elements field type.
  • I’ve tried the on_demand option for the filepicker (no luck).
  • Similar thing (data not loading) is happening with other dynamic fields using data-options@ which might be related.