QGraphicsScene fails to properly repaint the regions when setting QGuiApplication::setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy::PassThrough); and using fractional scaling with 4k display.

A way to reproduce:

Use Qt's "Drag and Drop Robot" example project for QGraphicsView.

Add the following lines to the very beginning of main():
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
QGuiApplication::setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);

Set the scaling for the Windows to 150%

Build and run the application.

Calling setViewportUpdateMode(QGraphicsView::FullViewportUpdate) on the view will remove this issue.