The following code shows all the problems I've found so far:

QWidget w2;
auto pal = qApp->palette();
pal.setBrush(QPalette::Window, Qt::green);
auto lay = new QHBoxLayout(&w2);
for (auto orientation : { Qt::Horizontal, Qt::Vertical }) {
    for (auto tickPos : { QSlider::NoTicks, QSlider::TicksBothSides , QSlider::TicksAbove, QSlider::TicksBelow }) {
        auto s = new QSlider(orientation);
        s->setTickPosition(tickPos);
        s->setAutoFillBackground(true);
        s->setPalette(pal);
        lay->addWidget(s);
    }
}
w2.show();

This results in the following output:
While this looks not that bad, there are several problems better visible when using QT_SCALE_FACTOR=3:

• the handle is cutted off on the left with QT_SCALE_FACTOR=1
• the groove is too long in the left with QT_SCALE_FACTOR=3
• the groove is not centered when no tickmarks are shown with QT_SCALE_FACTOR=3
• the tickmarks are not fully visible
• the handle is drawn in different sizes, the drawing does not fully comply with the style as the style does not draw an inner circle with controlStrokeSecondary
• the groove has a small outline with frameColorLight which is also not compliant to the style: