When creating an illustration, and using section view of the model, capping the section does not affect to the SVG export in any way.
Creo Illustrate needs to cap the section when exporting to SVG as well. The lines behind the capped geometry are visible in the SVG export, but not in the illustration.
Attached are the capped section.png which shows what is the illustration setup, and SVG export that has been done from the illustration.
Related PTC Case: CS257887
CS257887 is not PTC Support Case, it is TSS document, only.
You have to open Case at PTC Support and discuss the problem with them. Maybe they accept the problem as a bug...