I am running Intellitrace inside a Cloud Services instance. I have done so for a year or two and love it. I have done various updates including Windows from 8 - 10, Visual Studio to 2015 and its behaviour has changed and I don't know why.
One of the main benefits of it once you have pulled your historic data from Cloud Services you could double click on the error and it would take you to the code line which generated it.
In this case a Null Reference exception. It now opens up a diagsession with the exception in the Calls list but I can't dig any further.
By Calls list, do you mean the event table in diagsession. Please look at the screenshot at (in Events details section) https://blogs.msdn.microsoft.com/visualstudioalm/2015/01/16/intellitrace-in-visual-studio-ultimate-2015/
If so, you can 1. Double click the row with NullReferenceException thrown event. or 2. Click the row with NullReferenceException thrown event. Then click "Activate Historical Debugging" hyperlink. Both take you to historical debugging mode.
The UI has changed. It used to take you to historical debugging mode when you just click the row in the IntelliTrace window. Now you have to do either one of the above action.
Keep in mind that if it doesn't find the symbol and source file, it won't take you to the code line.