Randomly load custom post type data- code by Piet Goosen to https://wordpress.stackexchange.com/a/218760/12260

functions.php

<?php

/***
* Get the random custom post type ids and store them in a transient
*/
function get_random_id( $post_type = '' )
{
    $q = [];

    // Make sure we have a post type set, check if it exists and sanitize
    $post_type = filter_var( $post_type, FILTER_SANITIZE_STRING );

    if ( !$post_type ) 
        return $q;

    if ( !post_type_exists( $post_type ) )
        return $q;

    // The post type exist and is valid, lets continue
    $transient_name = 'rand_ids_' . md5( $post_type );

    // Get the transient, if we have one already
    if ( false === ( $q = get_transient ( $transient_name ) ) ) {
        $args = [ 
            'post_type'      => $post_type,
            'posts_per_page' => -1,
            'fields'         => 'ids', // get only post ID's
            // Add any additional arguments
        ];
        $q = get_posts( $args );

        // Set the transient
        set_transient( $transient_name, $q, 30*DAY_IN_SECONDS );    
    } // endif get_transient

    return $q;
}

/***
* The transient is set for 30 days, so we need to flush and recreate the transient as 
* soon as we publish a new custom post type post.
*/
add_action( 'transition_post_status', function ( $new_status, $old_status, $post )
{
    // Make sure we only target our specific post type
    if ( 'advertising' !== $post->post_type )
        return;

    global $wpdb;

    // Delete the transients
    $wpdb->query( "DELETE FROM $wpdb->options WHERE `option_name` LIKE ('_transient%_rand_ids_%')" );
    $wpdb->query( "DELETE FROM $wpdb->options WHERE `option_name` LIKE ('_transient_timeout%_rand_ids_%')" );

    // Lets rebuild the transient
    get_random_id( $post->post_type );

}, 10, 3 );

injector-filtering-content.php

<?php
/***
* Advert injector filter `the_content` can look something like the following where one checks if ad is checked as 
* true to load, it is single and not admin to then get an array of the post IDs here using advertising as the CPT and
* then display content using an ACF field
*/
add_filter( 'the_content', 'prefix_insert_post_ads' );
function prefix_insert_post_ads( $content ) {

    // checkbox to show ad, default true
    if ( get_field('show_advertisement') ) {
        if (     is_single() && 
               ! is_admin() 
        ) {
            // Get the array of post ID's
            $post_type_posts = get_random_id( 'advertising' );
            // Make sure we have posts
            if ( $post_type_posts ) {
                // Get the post object of the id first in line
                shuffle( $post_type_posts );
                $random_ad = get_post( $post_type_posts[0] );

                // Display the post content
                $link = addhttp( get_field('advertisement_link', $random_ad->ID));
                $image = get_field('upload_advertisement', $random_ad->ID);
                // get html
                $ad_code = '<a href="'.$link.'" target="_blank"><img src="'.$image.'" /></a>';
                // show ad after # paragraphs
                $show_after = get_field('advertisement_show_after');
                // return appended $content
                return prefix_insert_after_paragraph( $ad_code, $show_after, $content );

            } 
        }
    } 
    return $content;
}

post-display.php

<?php
/***
* Display the post content using acf field. This can be used in the area where you want 
* to load the data. Just need to make sure the post ids were loaded
*/

$link = addhttp( get_field('advertisement_link', $random_ad->ID));
$image = get_field('upload_advertisement', $random_ad->ID);
// get html
$ad_code = '<a href="'.$link.'" target="_blank"><img src="'.$image.'" /></a>';
// show ad after # paragraphs