@nopea said:

Further on Topographer on SketchupPro 2019, an issue present on both Mac and Win, pressing the exit button forces the triangles back to the model. Is this also on issue on older versions of SU? Would it be possible to rid of this feature?

I get no error messages.

So I would like to have this:

[attachment=1:8obdu9lo]<!-- ia1 -->1.JPG<!-- ia1 -->[/attachment:8obdu9lo]

Put when I press the Exit tool I get this:

[attachment=0:8obdu9lo]<!-- ia0 -->2.JPG<!-- ia0 -->[/attachment:8obdu9lo]

The two modes can be toggled with the menu "Edit > Hidden Geometry".

I think TopoShaper just re-establish the Hidden Geometry mode that is in effect when you launch it.