Ember: type error, *** is not a funciton

I have an ember application, pretty huge. The problem now is when I get into the Posts page, when I click a certain post, it throws error "TypeError: .default.* is not a function. For the third placeholder, I tried using different methods like findBy, getRecordby, It always throw the same error with the third placeholder replaced by the method I've tried.

It happened in the post route's aftermodel hook.

afterModel: function() {
        if (!user.get('isNew')) {
            return Model.getById(user.get('id')).then(function(profile) {
                user.populatePD(profile);
            });
        }
    },

can somebody tell me what's going on. Thank you so much.