On the right side of the Detail View is a panel that displays a comment box and a history/log for the Issue:
Comments—Use the Comments box to enter comments on the Issue. Be explicit with your entries to indicate changes made and the rationale behind the changes. Also, Comments is an excellent way to track remediation progress.
Comments Log—Below the new comment box is a timeline history of any changes to the Issue’s Priority, Progress Status, Assignee, Activity Status, and who made the change. Also, any comments added are included in the Comments Log.