Could you please tell me what I need to edit in the database if that's the case here?
Nothing is need for edit in DB ... I say first time for compare with CATEGORIES_TABLE and IMAGES_TABLE (cat_id for both table and image_thumb_file and image_media_file for IMAGES_TABLE) with FTP image file you have.
cat_id = folder create for upload.
image_media_file = data/media
image_thumb_file = data/thumbnails.
After use images gallery diagnostic, is say error for
file to see in DB 'or' FTP. No need for search hours with this. Error report is say source to you for look in DB 'and' FTP. Before my diagnostic, is terrible for user try to restore gallery. Now, is easy.