the url reads
http://domain.com/whatever-your-shortcode-page-is-called/page/2/
So presume your page is called “topics”
The code works – I’ve just retested it on twentyten site and pagination and subsequent pages were fine, so suggest you try
Check other plugins
Check that no other plugins are affecting this.
Turn off all other plugins, and see if that fixes the problem. If the problem is resolved, add back one at a time to see which is causing the conflict.
Check themes
If plugins are not the cause, the it may be a theme issue. Switch to a default theme, such as twentytwelve, and test.
and then come back if you need further help.