You've either:
  1. Accidentally messed up the {{ xyz }} values or the links/ buttons of your email template.
  2. Changed the language of your event.

Quick fix

  1. There is now a Reset Email Templates button which you can access by heading to Event Setup > Email Templates.
  2. This button resets all email templates back to their defaults which enabling you to revert back to the initial HeySummit email template.
  3. Do note that if you change the language of your event, while the uneditable email blocks will automatically be changed to the new language, the editable blocks of the email may not (in order to preserve your customisations).
  4. The reset button will then reset the templates back to the defaults for the new chosen language.