The issue likely arises because, when the post is created programmatically, the event_date field is not fully recognized by WordPress until the post is saved manually. This can happen if the date value isn’t stored correctly in the database, or if it’s missing necessary metadata or cache refresh. Here are a couple of solutions to ensure the date is stored and recognized correctly for sorting:

1. Use update_field Function for ACF Field When creating the post programmatically, instead of updating the ACF field using generic update_post_meta, try using the ACF-specific function update_field. This helps ACF recognize and format the date field properly.

$event_date = '2024-10-31'; // Example date format 'Y-m-d' update_field('event_date', $event_date, $post_id);