You have to check for the parameter 'start date' in your Workflows. I saw that you have assigned it to a new Workflow template you created. Without that parameter in your tasks/checklists the entries will not be shown in the workflow list!
If you change this you will see the 'start date' parameter in your task template again when you create a new task.
Unfortunately all the tasks created since this parameter was missing cannot be shown any more (unless you would like to change the code).