Navigation Not Working Properly

Since upgrading to the WordPress Twenty Twelve theme the page navigation for the series no longer works properly.

Let me explain:

Take this series https://brucegerencser.net/series/fundy-world-tales/

The link properly displays the first ten posts in the series. (my default posts per page in WordPress is ten)

However, when I hit the Load more posts button at the bottom, it starts to process, but does not advance to the next set of posts. (there are seventeen posts in this series) The button also disappears.

I get the same response using the series widget.

Suggestions?

Thank you for your help.

Bruce

https://www.ads-software.com/extend/plugins/organize-series/