Problem

In exports, certain Scroll versions placeholders do not work.

Explanation

This is probably because you are exporting from the Scroll Versions public view. When exporting a page from or Reader View (>Scroll Versions 3.0), only these placeholders are resolved: 

PlaceholderRendered value
$scrollVersions.Version.Idcurrent
$scrollVersions.Version.NameCurrently Published
$scrollVersions.Version.Descriptioncurrently published version

Solution

Export from the normal Confluence page view, rather than the public view.