The migrate_drupal_ui module now includes field plugins when looking for the source and destinations modules for an upgrade path when building the upgrade confirmation form. A module implementing Drupal-to-Drupal migrations should add source and destination module information to all migration field plugins.
Source and destination module information is added to the annotation of the field plugin.
Field plugin
If your migration uses a custom field plugin (defined in your module), add source_module and destination_module to the field plugin annotation.
Previously:
* @MigrateField(
* id = "image",
* core = {7}
* )
Now:
* @MigrateField(
* id = "image",
* core = {7},
* source_module = "image",
* destination_module = "file"
* )
An example of how to update and even add tests to demonstrate the issue can be found over in #2920118: Update cck and field migration plugin.