Issue
Sometimes a Nintex workflow does not start after a delay action or any timer service actions like "Check in", "Check out" or "Task Lazy approval"
Resolution
The first thing to check is that the "Workflow" SharePoint Timer Job Definition is started and enabled on the web application.
Steps:
Go to Central Admin -> Monitoring ->
Find your stalled Timer Job which is called "Workflow"
Check Job Status -> Find your Timer Job -> Click "Enable" and Run Now and verify that it executes successfully