If you can upload the model, we can provide a definite diagnosis, but here are some guesses.
You don’t say whether you are using perspective or parallel projection. Particularly in parallel projection it is possible to encounter clipping in the display as you orbit, zoom, or pan. If you search for “clipping” on the SU help or forums such as this one, you can find many discussions about clipping and how to mitigate it.
When zoom-extents causes a model to disappear, that most often means there is some bit of geometry placed far away from the rest. Zooming out enough to view everything at once makes everything too small to see! This problem is especially common when the model is imported from CAD, which has a tendency to place model contents far from the origin.
When orbiting, you often have to be careful to place the cursor over some part of the geometry before you start the orbit. Otherwise wild and large swings can occur because SketchUp can’t figure out how far behind the screen you meant to use as the center of rotation.