How to analize what causes the hang using instruments when actualy there nothing happens on main thread?

This is the part of the graph to detect what causes the hang using time Profiles with Instruments.

What actually takes that 516 ms?

I have studied this video tutorial from Apple but they focus on example when there is a lot of things, on main thread. In my example, I think it is not case... or I am wrong... I dont know. I need a quick clue to solve the problem, because this is quite annoying in the app. It happens quite often.