Scrolling a TAdvPdfViewer component

Scroll bars change when the mouse wheel is turned, but the view does not change, the PDF does not move up or down.
"PDFViewer.VerticalScrollBar.Position := PDFViewer.VerticalScrollBar.Position + 50;"
is no solution either.
Anybody knows what to do?

We have tested the demo here and couldn't see an issue. Please provide more information, a sample?

Everything works well with a multi-page document.
Load a single-page document, and zoom it up.