We solved this problem by this :
function acf_save_post( $post_id ) {
$file = get_field('upload_a_file', $post_id);
if( $file ){
$file_id = $file['ID'];
$post_to_update = array(
'ID' => $file_id,
'post_parent' => $post_id
);
wp_update_post( $post_to_update );
}
}
add_action('acf/save_post', 'acf_save_post', 20);
Replace upload_a_file with your correct acf field.
Basically we just modify the actual file post’s post_parent to the one it’s uploaded to.
