Error when getting data from MongoDB

Yesterday I faced with unusual behavior for MongoDB. So.. I store countries and languages with their codes in collections and when client side application need this data - it sends 'get' request to get data. It happens simultaneously

function init() {
            helperService
                .getCountries()
                .then(success)
                .catch(commonService.handleError);

            function success(res) {
                self.countries = res.data;
            }
        }
function init() {
            helperService
                .getLanguages()
                .then(success)
                .catch(commonService.handleError);

            function success(res) {
                self.languages = res.data;
            }
        }

Here I send request to get data in angular component $onInit

Backend code looks pretty simple:

var country = require('countryModel');
var language = require('languageModel');

function getCountries(req, res, next) {
  return country
    .find({})
    .then(success)
    .catch(next);

function success(data) {
    res.json(data);
   }
}

function getLanguages(req, res, next) {
  return language
    .find({})
    .then(success)
    .catch(next);

function success(data) {
    res.json(data);
  }
}

Locally all works as expected. But after deploying application on linux server I often see error 404 'Cannot GET /api/language' and 'Cannot GET /api/country'. Sometimes I got data but more often I got one error or this two errors above. Could anybody give me idea what is wrong?