All sites search scope returns results, This Site scope returns no results

I had an interesting issue at the customer. When searching through the search center (all sites scope) it returned results from site X. However, when I did the same query in the This Site:X scope, I had no results returned. The full crawl and the incremental crawl did work fine (as in that case All Sites wouldn’t return results anyway). As it turns out this is also related to the loopbackcheck issue in IIS/SharePoint. If you see this behavior on your SharePoint environment you should see acces denied errors popping up in your event viewer and you can refer to this post to fix it: https://koenvosters.wordpress.com/2009/06/15/access-denied-when-using-hostname-search-and-site-on-moss-2007/