$_FILES empty on created_{taxonomy} and create_{taxonomy} yet is is not on edit_{taxonomy}
This is just a half answer, but I wanted to share my findings. When adding a new term via the Add Term screen /wp-admin/edit-tags.php?taxonomy=work_type&post_type=work, AJAX is being used and it is not handling the $_FILES array, so it is empty. If you disable JS in your browser temporarily, then reload the page, add a new … Read more