Fixed the issue – thanks!
The comments plugin calls get_comment_author_link() function to either get comment’s URL or author’s name. The theme I am using, flavor, breaks this function by defining its own that functions improperly. We commented out the theme’s own get_comment_author_link function() but it’s only a short-term fix that will get overwritten upon theme’s update or may break something the theme relies on. I contacted the theme developer and asked them to fix author_link_new_window() and or make the theme compatible with plugins that call get_comment_author_link(), such as comments widget plus.