Even if 3D Cutaway is on, you may wish to hide the Cutting Planes.
Use the Show Cutting Planes toggle from the drop-down 3D Cutaway menu of the Standard toolbar.
The 3D Cutaway is in effect, but the Cutting Plane and the tabs are hidden, except for the tab at the top of the screen.
To show the Cutting Planes again, click the toggle command or the eye icon at the top of the screen.