There have been lots of reports like this, but those threads are closed. I’m uploading a very simple but busy model of a 2D floor-plan that causes the problem, FYI. When this happens, the saved model is also bad, and when I try to Open the original model, it’s bad also. However, if I close Sketchup, and double-click the original model, Sketchup reopens and opens the original model successfully (thank God). Of course, if I click Zoom Extents, it’s a rinse-lather-repeat.
Update: I guess I won’t be uploading the model, can’t find any upload dialog.