Do you have the viewport set up correctly in the first place? Is the scene in SketchUp set up with the camera set to Parallel Projection?
When you make any changes to the various sections of the Sketchup Model panel for a viewport, those settings override the settings for the scene. So, if you do something to override the camera position or any other camera settings (the Camera section of the SketchUp Model panel shows dark gray and there's a Reset button available) those settings will override the settings even if you select another scene. This is actually very useful but if you are copying a modified viewport to make another viewport, you'll need to click Reset for at least the Camera section in order to show the desired scene. Best workflow is to avoid making any camera changes that result in the dark gray background and Reset button showing. if you need to change the camera position or zoom level for the viewport, do that in SketchUp. You can drag the edges of the viewport to crop or show more of the view and you can adjust scale without modifying the Camera settings, though.
