Gantt Suite for Jira v 1.12.x Links configuration

Links configuration defines where to store links between Gantt chart tasks. Select None if you don’t plan to use a particular kind of link. The minimum setup usually requires at least End to start link.

Hierarchy link is need for child / parent relationships between arbitrary tasks. Multiple levels of hierarchy are supported.
Jira sub-tasks are always shown as children of their parent issue, and don’t need Hierarchy link setup for this.