Maia-90.137 - CTRL-H on interface Vladimir Goncharov Created November 03, 2009 21:58 CTRL-H on interface doesn't show implementing classes and inherited interfaces
I'm sure it is issue IDEA-25228 Hierarchy Callers does not work (Ctrl-Alt-H) (Idea 9)
I faced the same behaviour both for Hierarchy Callers and just class Hierarchy.
Try 'right arrow' to open the tree root in Hierarchy panel.