Facebook recently increased the restrictions on group events which means that a “User” Access Token is now needed in order to display them. You can obtain a long-term User Access Token by following the directions on this page. It involves setting up a Facebook “App” and then using that information to obtain your User Access Token at the bottom of the page.
We apologize for the inconvenience, Facebook changes are out of our control but we’ve done our best to find a workable solution. We’ve put together step-by-step directions at the link above but are always happy to help if you have any questions or issues along the way.