diff --git a/Public/TableOfContents/Infrastructure/Ui/TableOfContentsRenderer.php b/Public/TableOfContents/Infrastructure/Ui/TableOfContentsRenderer.php
index 5e425ab8..98afecb2 100644
--- a/Public/TableOfContents/Infrastructure/Ui/TableOfContentsRenderer.php
+++ b/Public/TableOfContents/Infrastructure/Ui/TableOfContentsRenderer.php
@@ -128,10 +128,21 @@ final class TableOfContentsRenderer implements RendererInterface
 
         error_log("{$debugPrefix}: post_id={$post->ID}, raw_content_length=" . strlen($post->post_content));
 
+        // Check if raw content has headings
+        $rawHeadingCount = preg_match_all('/<h[2-6][^>]*>/i', $post->post_content, $rawMatches);
+        error_log("{$debugPrefix}: raw_headings_count={$rawHeadingCount}");
+
         $content = apply_filters('the_content', $post->post_content);
 
         error_log("{$debugPrefix}: filtered_content_length=" . strlen($content));
 
+        // Check if filtered content has headings
+        $filteredHeadingCount = preg_match_all('/<h[2-6][^>]*>/i', $content, $filteredMatches);
+        error_log("{$debugPrefix}: filtered_headings_count={$filteredHeadingCount}");
+
+        // Log first 500 chars of filtered content for diagnosis
+        error_log("{$debugPrefix}: filtered_content_preview=" . substr(strip_tags($content), 0, 300));
+
         $dom = new DOMDocument();
         libxml_use_internal_errors(true);
         $dom->loadHTML('<?xml encoding="utf-8" ?>' . $content);