update_post_meta and update_field ony working when saving the post

I use Advanced Custom Fields (ACF) to store data in a custom field. I had latitude and longitude information stored separately, but I they need to be in one custom field so I made the function below. $query just queries all the relevant posts.

<?php 
$query = query_custom_posts(); if($query->have_posts()): 
while ($query->have_posts()): $query->the_post();
if(get_field('map_lat') && get_field('map_lng')):

$lat = get_field('map_lat');
$long = get_field('map_lng');
$coord = $lat.','.$long;
$post_id = get_the_ID();

update_post_meta($post_id, 'map_coor', $coord);


endif; endwhile; wp_reset_query(); endif;

?>

Now the function above works. The field map_coor gets populated with the lat and long separated by a comma (I can see the information in the field).

The weird thing is that if I use get_field('map_coor') on the front-end nothing shows up. If I save the corresponding post, then the info DOES show up.

In the function above I also tried to use the function update_field (from ACF) like this: update_field($post_id, 'map_coor', $coord) but the problem is still there.

So my question is; do I need to alter the function above or just run a function which saves all posts? If the latter is the case; how do I do that? I’ve found the hook save_posts but I’m not sure how to let it run through all the posts.

The problem is that the function update_field from ACF works a little bit different from update_post_meta. Can you see it?

update_post_meta( $post_id, $meta_key, $meta_value, $prev_value );
update_field( $field_key, $value, $post_id );

If you use update_post_meta you should in my opinion use get_post_meta to get the meta. If you use update_field you should use the_field or get_field because ACF stores the key/values-pairs in a slightly different way.