Update posts after populating ACF field value [closed]

This is the normal behavior.

ACF field value will not be added directly in your post until you save it. I’ve been facing this “issue” lately.

this is because you have created your field after your posts. So, your posts don’t have the associated value.

load_field doesn’t add values on existing post, it only add your value on the post form edition.

What I suggest, is that you can do a one-shot function that update all your posts in a second.

foreach(get_posts($args) as $post) {
  $data[] = ... // your event data
  update_field('your_field_group', $data, $post->ID); 
}

be careful here, you might want to use add_row function instead of the update_field (depending on your needed)
https://www.advancedcustomfields.com/resources/add_row/