Custom (cck) fields are being ignored during the migration using migration-tools 4.x. Only title and body is imported. How do I fix this? I'm running a migration from Drupal 6 to Drupal 8, following roughly the advices in the http://pnijjar.freeshell.org/2017/drupal8-migrate/ guide. 

At the moment, only title and body for each node is being imported for each node, despite definitions being correctly put into the .yml files generated by drush migrate-upgrade --configure-only . See an example migrate_plus.migration.d6_node_event.yml below. 

I can't figure out what is wrong. 

uuid: 51bc9a5e-6caf-4b7a-9b08-e34312467c89
langcode: en
status: true
dependencies: {  }
id: d6_node_event
class: null
field_plugin_method: null
cck_plugin_method: null
migration_tags:
  - 'Drupal 6'
migration_group: migrate_drupal_6
label: 'Nodes (event)'
source:
  plugin: d6_node
  node_type: event
process:
  nid: tnid
  vid: vid
  langcode:
    plugin: default_value
    source: language
    default_value: und
  title: title
  uid: node_uid
  status: status
  created: created
  changed: changed
  promote: promote
  sticky: sticky
  body/format:
    plugin: migration_lookup
    migration: d6_filter_format
    source: format
  body/value: body
  body/summary: teaser
  revision_uid: revision_uid
  revision_log: log
  revision_timestamp: timestamp
  field_organization:
    plugin: iterator
    source: field_organization
    process:
      value: value
      format:
        -
          plugin: static_map
          bypass: true
          source: format
          map:
            - null
        -
          plugin: skip_on_empty
          method: process
        -
          plugin: migration
          migration:
            - d6_filter_format
            - d7_filter_format
          source: format
  field_startend:
    plugin: iterator
    source: field_startend
    process:
      value:
        plugin: format_date
        from_format: U
        to_format: U
        source: value
  field_event_venue:
    plugin: iterator
    source: field_event_venue
    process:
      value: value
      format:
        -
          plugin: static_map
          bypass: true
          source: format
          map:
            - null
        -
          plugin: skip_on_empty
          method: process
        -
          plugin: migration
          migration:
            - d6_filter_format
            - d7_filter_format
          source: format
  field_event_speakers:
    plugin: iterator
    source: field_event_speakers
    process:
      value: value
      format:
        -
          plugin: static_map
          bypass: true
          source: format
          map:
            - null
        -
          plugin: skip_on_empty
          method: process
        -
          plugin: migration
          migration:
            - d6_filter_format
            - d7_filter_format
          source: format

...
What version of migrate_upgrade are you using? I see things like

      plugin: migration
      migration:
        - d6_filter_format
        - d7_filter_format


there, but --configure-only should have generated

      plugin: migration
      migration:
        - upgrade_d6_filter_format
        - upgrade_d7_filter_format