I've installed Portfolio and configured my Hierarchy in settings so that the Issue Type called "Product Requirement" is at the highest above Epics (see below).
I then went ahead and updated the "Parent Links" for a few Epics to the desired "Product Requirement" issue key. (see below)

However, when I click into that parent Issue Type (e.g. PR-257), the "Child Issues Section" is completely empty (see below).

Any idea why this is happening?
Additionally, these hierarchy issue types are not showing up in my Portfolio for Jira Plan either (see below)
