A bug in Google has wiped out a search feature that allows searchers to search within a specific site from the Google search result snippets. The feature launched three years ago, and it is officially called a Sitelinks Searchbox, where Google will show a search box directly within a search result snippet, allowing the searcher to restrict their search results to pages within the site listed.
Here is what it looked like on a search for “YouTube” when the feature launched.
Now, the Sitelinks Searchbox is no longer showing, at least temporarily. RankRanger caught the feature dropping out of Google globally a couple of days ago.
Google is working on it, but there is no estimated timeline for a fix to be rolled out.
Postscript: On October 3, 2017 the search box returned to the Google search results.