Renderer shows empty pages if the document is larger than 30 pages

[DStreichert]

If the document is larger than 30 pages, the first pages will be blank or white.
When I look at the file in another viewer, the first pages are definitely not empty.

This my XAML:
<ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" Margin="5">
<WindowsFormsHost>
<pdfiumViewer:PdfRenderer x:Name="pdfviewer" Enabled="True" Visible="True" />
</WindowsFormsHost>
</ScrollViewer>
and the code that load:
this.pdfviewer.Load(PdfiumViewer.PdfDocument.Load(this.tempFile));

What could I do wrong and how could I correct it?