title: Typo3 tx_news extend with custom Fields - Content disappears sometimes, caching Issue?
body: <p>I'm using Typo3 9.5.5 and I extended the extension tx_news with some custom fields.
  Everything works fine in front-end and back-end, but sometimes the custom content disappears in front-end and is not shown. Also the debug doesn't show the content. In my opinion it could be a caching problem, because after clearing the complete cache, the custom content is shown again.
  How can I fix this issue?</p>
  
  <p>I tried to put the needed templates into my custom extension, but the result is the same.</p>
  
  <hr>
  
  <pre><code>&lt;?php
  
  namespace myName\NewsExtend\Domain\Model;
  
  /**
   * News model for default news
   *
   * @package TYPO3
   * @subpackage tx_news
   */
  class NewsExtend extends \GeorgRinger\News\Domain\Model\News  {
    /**
     * @var string
     */
   protected $categoryHeader;
  
   /**
    * @var string
    */
  protected $issue;
  
  /**
   * Get categoryHeader
   *
   * @return string
   */
  public function getCategoryHeader()
  {
      return $this-&gt;categoryHeader;
  }
  
  /**
   * Set categoryHeader
   *
   * @param string $categoryHeader categoryHeader
   */
  public function setCategoryHeader($categoryHeader)
  {
      $this-&gt;categoryHeader = $categoryHeader;
  }
  
  /**
   * Get issue
   *
   * @return string
   */
  public function getIssue()
  {
      return $this-&gt;issue;
  }
  
  /**
   * Set issue
   *
   * @param string $issue issue
   */
  public function setIssue($issue)
  {
      $this-&gt;issue = $issue;
  }
  
  }
  </code></pre>