We sent a mass mailing under 5.27.0 (Wordpress) and the email Click Through links were invalid as noted earlier. They did however include our domain.
We upgraded to 5.27.3 and the links are still invalid. They appear to be missing our domain, e.g.
http://?civiwp=CiviCRM&q=civicrm/mailing/url&u=674&qid=63201