title: Excel freezes when expanding group of rows with conditional formatting
body: <p><strong>Issue:</strong> Excel freezes when expanding group of rows which contain conditional formatting. I can save using <code>CTRL + S</code>, but worksheet functionality and toolbar buttons lock up.</p>
  
  <p><strong>Working solution:</strong> Deleting the conditional formatting, which consists of:</p>
  
  <ul>
  <li>Rule: <code>=AND($C7&lt;&gt;"",$C7&lt;&gt;0)</code></li>
  <li>Applies to: <code>=$C$7:$AB$84</code></li>
  </ul>
  
  <p><strong>Excel version:</strong> Excel 2016</p>
  
  <p><strong>File Type:</strong> .xlsb</p>
  
  <p><strong>Background details:</strong> Rows were initially grouped with a macro. VBA code which groups the rows:</p>
  
  <pre><code>ws.Range(ws.Cells(firstRow, 1), ws.Cells(lastRow, 1)).Rows.Group
  ws.Outline.ShowLevels RowLevels:=1
  </code></pre>
  
  <p><code>Screenupdating</code> is set to <code>True</code>. There are no other row groups. Beyond failure to expand the group, I have not come accross any other issues with the file.</p>
  
  <p>How can I prevent this without deleting the conditional formatting?</p>