All XTools Blame and Authorship pages currently don't work, because Wikiwho returns 500s. For instance at https://wikiwho.wmcloud.org/en/api/v1.0.0-beta/rev_content/Death/?o_rev_id=true&editor=true&token_id=true&out=true&in=true. I don't think it's because of the request parameters, because that url is straight from the doc (it's not exactly the one XTools uses). Tested with different pages and languages.

Off of the top of my head, could perhaps be related to lack of a proper user agent (these days T400119 is happening)?