A project with 'todo' lower case in the source code.
Jenkins configured to scan for 'TODO' upper case but with 'Ignore case' option selected.
On the project summary page, the graph indicates the correct number of TODO items. When you click on the graph to view the details, all the subsequent views are missing the lower case items.
As a workaround, I entered 'TODO, todo' in the Task Tags field, but this would miss mixed case in the source.