Rowspan generates an error during generation and is not displayed in the PDF output

When I create a table with a rowspan="2", I receive an error message in the log (Incorrect link). In addition, the chapter is not displayed in the PDF output.

<table class="GreyHead">
    <caption>Gerätevarianten</caption>
    <colgroup>
      <col width="20%" />
      <col width="15%" />
      <col width="15%" />
      <col width="15%" />
    </colgroup>
    <thead>
      <tr>
        <th colspan="1" rowspan="2"><p>Artikelbezeichnung</p></th>
        
        <th colspan="2" rowspan="1">
          <p class="centered">Kupfer-Ports</p>
        </th>
        <th>
          <p class="centered">SPE-Ports</p>
        </th>
      </tr>
      <tr>
        <th>10/100 MBit/s</th>
        <th>10/100/1000 MBit/s</th>
        <th>10BASE T1L</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td><span data-keyref="Produktbereich 1">Produktbereich 1</span></td>
        <td>
          <p class="centered"> </p>
        </td>
        <td>
          <p class="centered">3x RJ45</p>
        </td>
        <td>
          <p class="centered">8x SPE</p>
        </td>
      </tr>
    </tbody>
  </table>

If I remove the rowspan, everything is OK.