try viewing with Camera >> Perspective…
YES!!!JOHN_DRIVENUPTHEWALL thankyou from djs
If you want to understand why you sometimes see this, search this forum for Clipping. It’s a function of the OpenGL graphics engine that SU uses.
Basically it’s the camera not showing what is behind it (or in some cases what is in front of it, but super close). In perspective view, the mouse wheel moves the camera back and forth. In parallel projection it changes the size of the image plane, but keeps the camera on that plane.
Unfortunately, in SketchUp, in Parallel Projection mode, zooming in and out does move the picture plane. Probably the zoom tool uses behind the scenes same algorithms for both perspective and parallel. That is why you get clipping much more frequently in Parallel mode.
If zoom moved the camera back and forth in parallel projection it wouldn’t be visible to the user, other than clipping coming and going.