If the issue persists after downloading the October CU, it might be caused by a Microsoft SharePoint workflow engine bug. For more information, see SharePoint Workflow Engine bug. This known bug can affect some Nintex Workflow and cause them to freeze under certain conditions.
Test a basic SharePoint designer workflow with a delay. If your issue is also occurring in the SharePoint designer workflow, this suggests there is a greater issue with this service. Contact Microsoft Support for additional assistance.
Note: Nintex Workflow uses the SharePoint Workflow engine. If these issues are occurring in Nintex Workflows, they will also occur in SharePoint Designer workflow. Normally, a simple SharePoint Designer workflow with a Delay or Pause activity will result in the same behavior and this test can be used to demonstrate the problem requires Microsoft Support.