I think I know what might be happening. When you open the file in Navisworks it might be set to an Orthographic Projection. The "Walk" tool is Perspective Only, and when you change from an orthographic view to a perspective view in Navisworks, sometimes it realigns the camera position. So just click one of the Isometric Corners of the Viewcube to "realign" everything back into view. Also note, you can set a "Home View" too (little house icon to the top left of the Viewcube).
Hope this helps.