ACF fields don't show up when previewing draft posts. This is an ugly hack to try and overcome that situation.

wp-acf-overcome-draft-preview-issue.php

<?php
/**
 * ACF fields don't show up when previewing draft posts. This is an ugly hack to try and overcome that situation.
 */
function dctit_hack_preview() {
    $post_types = array ( 'post', 'page' );//add/edit/delete post types as needed
    global $post;
    
    if ( !in_array( $post->post_type, $post_types ) ) {
        return;
    }

    if(isset($_GET['preview'])){
        unset($_GET['preview']);
    }
}
add_action( 'wp', 'dctit_hack_preview' );