This Activity panel includes details of Issues raised and updated, as well as all activities relating to Tasks within the Event. For example all Task State transitions are recorded within the Activity Panel.

The Event Activity panel can be accessed from the Activity button in the Event panel, depicted by the flashlight icon.

From the report drop down you have the ability to view any changes which were made to Issues only, Stages only or Tasks only.  These reports allow you to focus on the changes which are most relevant to you.