When making manual changes to the Workflow definition, orphaned Workflow tasks may be created within the SharePoint environment. This can cause problems when responding to tasks through Nintex Mobile (the tasks are continuously recreated), as such it is important to remove these when they occur.
Removing orphaned tasks through the GUI:
1. Navigate to your SharePoint site
2. Choose to edit the page
3. Select insert => Web Part. From the Categories column select Nintex Workflow 2013(or 2010) and from Parts column select My Workflow Tasks
5. Once the web part is added press Save button.
6. You know must be able to see a list of tasks assigned to you in the web part
7. The ones which have Remove task link button are orphan tasks and you can delete them by clicking on the link
8. if you don’t see them in the first page, make sure you navigate to all pages and delete them all. Unfortunately the this moment there is no way to delete them all in one go and you need to do this one by one by one
9. Go back to your Nintex Mobile, Delete Local Storage and you should not see the tasks anymore