Ajax load more posts - WP_Query parameters not working

Question

I'm trying to replace the standard WP pagination with an Ajax load more posts button. I'm basically following the code from this question which for the most part works well.

Here's the relevant code:

HTML (blog index page):

<div id="content">

<?php $args = array(
    'posts_per_page' => 5
);

if (isset($_GET['views'])) {
  $args['orderby'] = 'meta_value_num';
  $args['meta_key'] = 'post_views_count';
  $args['order'] = 'DESC';
};

$wp_query = new WP_Query($args); ?>

<?php while( $wp_query->have_posts() ): $wp_query->the_post();  ?>
    <?php the_title(); ?>
<?php endwhile; ?>  

<a id="more_posts">Load More</a>

<?php wp_reset_postdata(); ?>

</div>

JS (at the bottom of blog index page):

var ajaxUrl = "<?php echo admin_url('admin-ajax.php', null); ?>";
var page = 1; // What page we are on.
var ppp = 4; // Post per page

jQuery("#more_posts").on("click",function(){ // When btn is pressed.
    jQuery("#more_posts").attr("disabled",true); // Disable the button, temp.
    jQuery.post(ajaxUrl, {
        action:"more_post_ajax",
        offset: (page * ppp) + 1,
        ppp: ppp
    }).success(function(posts){
        page++;
        jQuery("#content").append(posts);
        jQuery("#more_posts").attr("disabled",false);
    });

   });

PHP (in functions.php):

function more_post_ajax(){

$offset = $_POST["offset"];
$ppp = $_POST["ppp"];
header("Content-Type: text/html");

$args2 = array(
    'posts_per_page' => $ppp,
    'offset' => $offset,
    'orderby' => 'rand'
);

$custom2 = new WP_Query($args2);

while ($custom2->have_posts()) : $custom2->the_post(); 
   the_title();
endwhile;

exit;
}

add_action('wp_ajax_nopriv_more_post_ajax', 'more_post_ajax'); 
add_action('wp_ajax_more_post_ajax', 'more_post_ajax');

What I need to do is alter the parameters of the query used to load the posts based on whether 'views' is selected as the order, as it works in the template file's code.

Everything works as its should, except that arguments added to the query in functions.php are not working correctly. For example, if I change posts_per_page from the $ppp variable to a number in functions.php, that will work correctly. But, 'orderby' => 'rand' (just being used for testing purposes) does nothing, the posts are still loaded by date. Any other orderby or other parameter I've tried does not work. If I take the query out of the function and add it directly to the template file, it works fine.

Why is the query in functions.php not recognizing additional parameters? Why does changing posts_per_page or offset work correctly, when other parameters don't?

Answer 1

For whatever reason, it was an issue specific to the orderby parameter. Adding remove_all_filters('posts_orderby'); to the top of the more_post_ajax() function solved the problem.