I was just working on a really basic model and suddenly there appeared this section plane and I couldn’t get a hold on it to remove it. I recently updated to 16.1.1449. The link to the file below is a very simple file with the section plane cutting through anything and everything in either layer.
Your camera was set to Parallel Projection, which is prone to clipping.
Click … Camera > Perspective to regain a normal perspective view of the 3D SketchUp world.
The camera Field of View (FOV) was set very wide … to ~90°
For general modeling a 35° FOV provides a normal perspective view of the 3D SketchUp world.
Click … Camera > Field of View and type 35 and then press Enter to reset the FOV to the default 35° FOV