Due to a breaking change made in the release of Cornerstone 3.0, you can no longer load Cart resource on non-cart pages in the Cornerstone theme PR #1401.

While the theme itself doesn’t depend on this resource on non-cart pages, this can potentially affect any scripts added by the Script Manager or the legacy footer scripts that depend on cart.

If this applies to you, you will want to add the cart resource back on the page types that need it (via front matter).