Search Without result with parameter &u=site

Go to Central Administration >> Application Management >> Manage service applications >> Search Service Application >> Content Sources >> At Local SharePoint sites on Menu context click Edit

If you crawl content of the original site => have result

Result as:

If you only crawl original site

Result as:

If you only crawl Extend site and don’t crawl original site

Don’t have result:

But if you delete the URL after &u= then enter will have result

Conclusion: you must crawl original site