Geopak SS3 Cross Sections - Plot a Tin on existing sections

I am running Geopak SS3. I have created Cross Sections using the "Create Cross Sections" tool under corridor.

The Sections look good.

I created a proposed tin from corridor and I want to check it by plotting the proposed tin as existing ground on the existing cells.

When I plot the proposed tin using the old method, the proposed tin does not plot. I do not know why.

If I use Geopak SS2, the proposed tin plots fine.

Why can't  I do this in SS3?

Thanks for you help,

Phil