What is the bug in fancybox 1.3.4?

Question

JavaScript

I support a project with legacy code.
Upgrading is currently not possible.
When you click on the link, you need to display a pop-up window, on the first click everything works, on the second and subsequent, an error pops up:

Initialization:

jQuery(function($){
  $(document).ready(function(){
    $('.fan').fancybox();
  });
});

fancybox version: 1.3.4
jQuery version: 1.12.4
jQuery Migrate version: 1.4.1