Lets take a look to an standard example from Qt called "svgviewer":
1) This is how my SVG image looks in this example in Qt 5.6.3

2) This is how my SVG image looks in this example in Qt 5.9.1

I will add an example and my SVG image into attachment. I do not know where things goes wrong in QGraphicsSvgItem on parsing phase or on drawing phase.