Nintex Workflow Stalling on Document Generation Action

I encountered an issue recently where a few Nintex Workflow 2013 workflows that had been running successfully for some time suddenly started stalling.  The workflows still showed a status of “In Progress” but were not moving forward.  Checking the Workflow Progress and Workflow Details pages showed no error messages or issues.  I finally noticed that these workflows were freezing when trying to execute a Document Generation workflow action.

After investigating, I determined that the issue was related to a Nintex Workflow service not running in my SharePoint 2013 environment.  Specifically, the Nintex Workflow Start Service was not actively running on any of my SharePoint 2013 servers.  Once I restarted that service on one of my servers, the stalled workflows continued running, completed the Document Generation action, and progressed to the next workflow steps.