Inkscape error when converting from SVG to PDF

With the QSvgGenerator, I created a .svg to export some QGraphicsItems on my QGraphicsScene:

QString fileName = QFileDialog::getSaveFileName(this, "Export to SVG", ".", "SVG (*.svg)\n");
QSvgGenerator generator;
generator.setFileName(fileName);
generator.setSize(...);
generator.setViewBox(...);
QPainter painter;
painter.begin(&generator);
scene.clearSelection();
scene.render(&painter);
painter.end();

The resulting .svg picture looks like the following (opened in Inkscape):

When I tried to export it as a .pdf file the resulting .pdf looks like this:

Can someone please make sense of this error? Here is a link to my .svg file.

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