Thumbnail olmayan yazıları göstermiyor demişsiniz

<?php
 
$markup_opt = basic_get_theme_option( 'schema_mark' ); // false or 0
$markup = ( is_single() && ( $markup_opt || false === $markup_opt ) ) ? true : false;
 
?>
 
      <?php
      if ( ! is_single() && has_post_thumbnail()) {
 
         $thumbnail_size = apply_filters( 'basic_singular_thumbnail_size', 'thumbnail' );
         $attributes     = apply_filters( 'basic_singular_thumbnail_attr', array('class'=>'thumbnail') );
 
         if ( has_post_thumbnail() ) {
            $show_thumb = ( get_theme_mod('show_mobile_thumb') ) ? ' show' : '';
            do_action( 'basic_before_post_thumbnail' ); ?>
            <a href="<?php the_permalink() ?>" title="<?php the_title_attribute(); ?>" class="anons-thumbnail<?php echo $show_thumb; ?>">
               <?php the_post_thumbnail( $thumbnail_size, $attributes ); ?>
            <div class=""><span><?php the_title_attribute(); ?></span></div>
            </a>
            <h2><a href="<?php the_permalink() ?>"  title="<?php the_title_attribute(); ?>" class"baslik">  <span id="ilk-b" class="yazi"><?php the_title_attribute(); ?></span>
            </a></h2>
 
 
            <?php
         }
 
      } else {
 
         do_action( 'basic_before_single_content' );
         the_content( '' );
         do_action( 'basic_after_single_content' );
 
      } ?>

if ( ! is_single() && has_post_thumbnail()) burada thumbnail kontrolü de ekledim bir kez daha deneyin bakalım..