unfurl.php never sets up the templater to have a non-null style, which means the master template is used instead of the visitor's style (either default or explicitly set). Additionally the 'xf' default template argument is not present.
I do not know if it is related to the above, but after upgrading to 2.2.7, unfurling on my XenForo forum has stopped working for links from some sites, while it still works for links from other sites. What could be the cause?