Hi maestroc
The problem seems come from the rockettheme Joomla template on your site, I see lots of JS conflict on that page.
I tried to assign Protostar template to that 'Register for a class' menu item and it shows normally: https://share.getcloudapp.com/OAubBlzy
You can try and see the same.
Please try to contact the provider of this Joomla template on your site for help to fix issue first.