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That's why it's 'loading...' and never show comment list?

1. Check footer.php file of your theme, if you cannot find <?php wp_footer(); ?>, please add <?php wp_footer(); ?> before </body>.
2. (If that's okay with step 1, ignore this.) Check the plugin settings on 'Settings -> WP-RecentComments', and reset JavaScript Lib to 1st or 2nd item.

Comments are messed up after update plugin?

1. Select 'Use wp-recentcomments.css' in 'Settings -> WP-RecentComments' page.
2. (If that's okay with step 1, ignore this.) Remove wp-recentcomments.css file in theme directory if it exists.