8 – “Can’t migrate source field body of type text_with_summary configured with plain text processing.”

I am trying to migrate a Drupal 7 site to Drupal 8, but I get the following error message.

Can’t migrate source field body of type text_with_summary configured with plain text processing. https://www.drupal.org/docs/8/upgrade/known-issues-when-upgrading-from-drupal-6-or-7-to-drupal-8#plain-text

I read the linked documentation page and changed the body field in every content type to filtered, but the error persists.

How can I resolve this issue?