After installation, Jira Administrator can decide if the graph should be visible or hidden by default (3). It could be done within "Apps" (1), after accessing "Settings" (2) (located under the "Issue Links Viewer" section):
This setting can be overwritten by user preferences - even if the graph is hidden by default, it can be displayed after pressing "Show links graph" button (1):
Expanded graph can be hidden again via "Hide" option in the top right corner (1):
