This seems like an unlikely scenario, but it popped up here at Indiana.
Create a gradebook item.
Add comments for student A
Delete the gradebook item.
Add a new gradebook item with the exact same name
Add comments for student A again
A call to GradebookService.getAssignmentScoreComment to retrieve the comment will result in an IncorrectResultSizeDataAccessException because the query (which uses the gb item name as the identifier) does not filter out deleted gb items.
The method is currently used by Forums and Assignment2. To see the issue in Forums, create a graded topic associated with the gb item above. Try to grade a post from Student A. Clicking the "Grade" link does nothing and there is a stack trace in the logs.