[5.7.0] Cannot access QML Scene3D/Entity reference from C++ code

When looking up for QML references by 'objectName' from C++ code, the returned pointer is always NULL. For example:

QQuickItem *scene3D = qobject_cast<QQuickItem*>(rootObject()->findChild<QObject *>("scene3DItem"));
QEntity *sceneEntity = qobject_cast<QEntity *>(scene3D->findChild<QObject *>("sceneRootEntity"));

This prevents any interaction between the QML and C++ world, thus it is not possible to manipulate a QML scene at runtime.

This happens either at startup when Component.onCompleted of scene3D is fired, or at runtime when calling a Q_INVOKABLE from QML asynchronously.

Please see attached examples:

• dynamic-scene-5.7.tar.gz exposes the plain issue
• dynamic-scene-cpp-qml-workaround.tar.gz tries to workaround the issue by passing QML references to the C++ invokable. This was working up to 3 days ago. As of today, it segfaults when requesting a scene re-render