accounts2.js

define("models/accounts2", [
  "lib/local-backbone",
  "lib/local-underscore",
  "models/accountProgress"
], function(
  Backbone,
  _,
  progressModel
) {
  var FlatAccounts = Backbone.Collection.extend({
    initialize: function(options) {
    
      // SETUP FOR ERROR:  
      // populate the 'planned' attr from account-progress
      var updatePlanned = _.debounce(this.updatePlans);
      this.on("add remove change:attributes.active", updatePlanned, this);
      progressModel.on("change", updatePlanned, this);
    },

    updatePlans: function() {
    
      // 
      // HERE COMES THE ERROR:
      // this.each throws 'undefined is not a function' (sometimes)
      
      this.each(function(model) {
        // do something
      }, this);
    }
  });



  return FlatAccounts;
});

And _.debounce(_.bind(this.updatePlans, this)) doesn't help?

Didn't digged into because I'm just on my phone. :)

yeah that has helped in other places, just stumped on where the issue is coming from: underscore or our code