Mega menu using nested ACF repeaters/flex

gistfile1.php

<?php
// check parent repeater
if( have_rows('parent_navigation_items', 'options') ):
 
  echo '<ul class="nav primary-header-nav">';

  // loop parent items
  while ( have_rows('parent_navigation_items', 'options') ) : the_row();
    
    echo '<li>';

      // Get parent item post object and link text
      $parent_post = get_sub_field('parent_link');
      $parent_link_text = get_sub_field('parent_link_text');

      // output parent link
      echo '<a href="' . get_permalink( $parent_post->ID ) . '">' . $parent_link_text . '</a>';

      // check if parent has child items
      if( have_rows('children') ):

        echo '<ul class="child_items">';

        // loop child items
        while ( have_rows('children') ) : the_row();

          // if highlight panel layout
          if( get_row_layout() == 'highlight_panel' ):
            
            // get highlight post object and panel text
            $panel_post = get_sub_field('panel_link');
            $panel_text = get_sub_field('panel_text');

            // output panel
            echo '<li class="panel">';
              echo '<a href="' . get_permalink($panel_post->ID) . '">';
                echo '<h3>'.get_the_title($panel_post->ID).'</h3>';
                echo '<p>'. $panel_text .'</p>';
              echo '</a>';
            echo '</li>';
       
          // endif highlight panel layout
          endif;

          // if mini image links (e.g. sector links) layout
          if( get_row_layout() == 'mini_image_links' ):

            // get mini links menu title
            $mini_link_title = get_sub_field('mini_images_title');

            echo '<li class="mini_images">';
            echo '<h3>'.$mini_link_title.'</h3>';
            echo '<ul>';

            // check if mini image links repeater has rows
            if( have_rows('mini_image_links') ):

            // loop mini image links repeater
            while ( have_rows('mini_image_links') ) : the_row();

            // get link post object, and set variable for mini image
            
            $link_post = get_sub_field('link');
            var_dump($link_post); // THIS RETURNS bool(FALSE) for each row (e.g. 8 times in this instance)

            /* COMMENTING OUT FOR DEBUG PURPOSES
            $link_post_menu_img = get_sub_field('main_menu_image', $link_post->ID);
            $link_post_banner_img = get_sub_field('banner_image', $link_post->ID);
            $link_post_image = ($link_post_menu_img != null ? $link_post_menu_img : $link_post_banner_img);

            // output panel
            echo '<li>';
              echo '<a href="' . get_permalink($panel_post->ID) . '">';
                echo '<figure>';
                //if($link_post_image){ echo '<img src"'.$link_post_image['sizes'][''].'" />'; }
                echo '</figure>';
                echo '<p>'.get_the_title($link_post->ID).'</p>';
              echo '</a>';
            echo '</li>';
            */
            // end mini image links repeater loop
            endwhile;

            // endif mini image links repeater has rows
            endif;

            echo '</ul>';
            echo '</li>';
       
          // endif mini image links layout
          endif;

        // end children loop
        endwhile;

        echo '</ul>';
      
      // endif has children
      endif;
  
    echo '</li>';

  // end loop parent items
  endwhile;

  echo '</ul>';

// no parent items 
else :

  echo 'nada';
   
// end if parent items
endif;
?>