@Oatmeal I guess you already solved your issue since 9 months passed but I experienced same issue today and solved it eventually so I want to share it anyway. Instead of using below code
self.setFlag(QGraphicsItem.ItemIsMovable, True)
self.setFlag(QGraphicsItem.ItemIsSelectable, True)
self.setFlag(QGraphicsItem.ItemIsFocusable, True)
self.setFlag(QGraphicsItem.ItemSendsGeometryChanges, True)
using below code did the trick for me
setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsMovable | QGraphicsItem.ItemIsFocusable | QGraphicsItem::ItemSendsGeometryChanges);