Unwanted slicing of my file

As I’m working along, usually orbiting, my drawn image appears to slice up in various unwanted and mysterious ways.
Screen Shot 2021-12-13 at 12.40.57 PM
I zoom in and out and wait a while and it all comes back without the slices. Very upsetting. Any idea what’s causing this?
Thanks,
Dick

You can search for “clipping” here in the forum.
Here’s an article from the help center:
https://help.sketchup.com/en/sketchup/clipping-and-missing-faces

Camera>Perspective
Camera>Zoom Extents

I would recommend, too, that you get used to working in Perspective mode. This happens much less there, and after a short time Parallel Projection starts to look as weird as it actually is.

Looking at the diverging parallels in your image, I am inclined like @Anssi to suspect you are modeling in parallel projection. The consensus among experts is that parallel is meant for 2D presentation of standard views such as front, top, right, etc., and that perspective should be used while creating or editing a model. It is as close as you can get to a real-life view of the model, whereas parallel is intentionally distorted to give an artificially flat view.