Add the following code just after UnderscoreJS declaration to find where _.template calls are run against empty templates.

underscore_template_err.js

/**
 * Add the following code just after UnderscoreJS declaration to find 
 * where _.template calls are run against empty templates.
 */
 
(function(old){
 
  _.template = function(str, data) {
    if(!str){
      console.error("Could not load template", new Error().stack);
      return;
    }
 
    return old.call(_, str, data);
  };
 
})(_.template);