To explore leaks, I followed several calls now I can't return to the root. I tried all the possible hotkeys and menu items.
Instruments, Leaks: How to return to the root of the Call Tree?
I think you're experiencing a bug in Instruments. Usually when you follow a call, an item gets added to the jump bar. Remove the item from the jump bar by clicking the X button to go back to the root. The jump bar in your screenshot having no items is a sign of a bug.