via make.wordpress.org => original post link
Note: This is adapted from a conversation that happened on the Make WP Slack (see the link for more context).
Our current situation regarding thumbnails
Thumbnails were collected by providers and put in the thumbnail column in the catalog. We have data there now, and the column has not been dropped. Since this column also exists in the API, the data from it (for both audio and image) gets copied into the thumbnail column there as well. However, only the Audio model uses the thumbnail column, the Image model ignores it and tries to create a scaled down thumbnail using the primary image URL. The MediaStore class in the provider has been modified so that no new thumbnail URLs can be added to the thumbnail column, but they can be added in the metadata under meta_data[“thumbnail_url”].