I have created one simple workflow on custom list using SharePoint designer 2013.While designing workflow, I have unchecked the “Allow this workflow to be manually started” and select rest two options like “Start workflow automatically when an item is created and Start workflow automatically when an item is changed”. And I logged in the site using system account. Workflow is configured for Item created and changed level.

So when I created new item in the list at that time workflow didn’t start automatically. After doing some research, I found that designer workflow will not start automatically if you logged in site as a SYSTEM ACCOUNT.

The root cause is sharepoint security engine didn't allow the workflow start automatically when you logged in site as a system account.