ACF Post Content Not Being Searched

Advanced Custom Fields does not automatically output the fields you add in the_content(). You need to use ACF’s template functions. Refer to the documentation for more.

Based on your comment, yours will look something like:

<div class="contentarea">
    <div id="content" class="content_right">
        <?php if ( have_posts() ) :
            while ( have_posts() ) : the_post(); ?>
                <div id="post-<?php the_ID(); ?>" class="posts">
                    <article>
                        <h4><a href="https://wordpress.stackexchange.com/questions/275813/<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></h4>        
                        <p><?php the_content();?></p>

                        <?php while ( have_rows( 'details' ) ) : the_row(); ?>
                            <?php the_sub_field( 'name' ); ?><br>
                            <?php the_sub_field( 'description' ); ?>
                        <?php endwhile; ?>

                        <a href="<?php the_permalink();?>">Read More</a>
                    </article>
                </div>
            <?php endwhile; ?>
        <?php endif; ?>
    </div><!-- content -->    
</div><!-- contentarea -->