In qquickpointerhandler.cpp, there're following lines in QQuickPointerHandler::handlePointerEvent().

event->setExclusiveGrabber(pt, nullptr);
onGrabChanged(this, QPointingDevice::CancelGrabExclusive, event, pt);

This seems that first, the grab event is ungrabbed (by setExclusiveGrabber() which emits UngrabExclusive ) and then cancelling the grab by onGrabChanged(this, QPointingDevice::CancelGrabExclusive, ...).

This mean, there can be a scenario that you are executing a grab changed when you do not have a grab, nor are getting one.