JsonPath parser error - can't reference feed entity

We've been using Feeds for a little bit and it's been working fine with RSS/Atom and QueryPath XML feeds, but I'm getting an error when trying to set up a JsonPath import.

I've got it set up with an initial set of mappings just to test it, but it constantly fails with errors like:

The content Take Action failed to validate with the following errors:
feeds_item.0.target_id: This entity (feeds_feed: 3) cannot be referenced.
Please check your mappings.

It's clearly parsing the data via the mappings because "Take Action" is one of the items being imported. What is weird is that it's the feed entity itself that should be written to the node__feeds_item table, in feeds_item_target_id. It says to check the mappings but the feed ID should just get applied, the mappings are for the Feed Item level (item URL and guid).

The exported config for my Feed Type is:

uuid: 48d4d3df-469a-465e-b620-b7ee6ac66693
langcode: en
status: true
dependencies:
  config:
    - field.field.node.alert.feeds_item
    - node.type.alert
  module:
    - feeds_ex
    - node
label: 'P2A campaigns'
id: p2a_campaigns
description: ''
import_period: 3600
fetcher: http
fetcher_configuration:
  auto_detect_feeds: false
  use_pubsubhubbub: false
  fallback_hub: ''
  request_timeout: 30
parser: jsonpath
parser_configuration:
  context:
    value: $..
  sources:
    __subtitle:
      label: $..subtitle
      value: $..subtitle
    __link:
      label: $..link
      value: $..link
    __id:
      label: $..id
      value: $..id
  display_errors: false
  source_encoding:
    - auto
  debug_mode: false
  line_limit: 100
processor: 'entity:node'
processor_configuration:
  update_existing: 2
  update_non_existent: node_unpublish_action
  expire: -1
  owner_feed_author: false
  owner_id: 0
  authorize: true
  skip_hash_check: false
  values:
    type: alert
custom_sources:
  __link:
    label: $..link
    value: $..link
    machine_name: __link
  __id:
    label: $..id
    value: $..id
    machine_name: __id
  __subtitle:
    label: $..subtitle
    value: $..subtitle
    machine_name: __subtitle
mappings:
  -
    target: title
    map:
      value: __subtitle
    unique: {  }
  -
    target: feeds_item
    map:
      url: __link
      guid: __id
    unique: {  }

thanks for any advice on fixing this!