Displaying objects in the 3D view may require re-centering the view.
There is a button in the 3D view widget for re-centering the view:
(extracted from How, from python-scritps, to trigger the click-function of "center of the 3D view on the scene"? - #8 by aiden.zhu)
You can use the following python snippet if you prefer to do that programmatically (from Script repository — 3D Slicer documentation):
layoutManager = slicer.app.layoutManager()
threeDWidget = layoutManager.threeDWidget(0)
threeDView = threeDWidget.threeDView()
threeDView.resetFocalPoint()