Smoothstate.js - removeClass not working onReady function

I'm using Smoothstate.js to add page transitions to my website and I'm trying to show a loading page between each page transition using the onStart, onProgress and onReady functions.

The code I have works, but every now and again it get's stuck on the loading page and the container div isn't removing the class 'is-loading'. However, it is removing the is-exiting class even though they're with the same removeClass line?

I'm so confused as to why It's not removing. Can anyone help please?

// Photoswipe
$(function(){
  'use strict';
  var options = {
    prefetch: true,
    debug:true,
    cacheLength: 0,
    repeatDelay: 500,


    onStart: {
      duration: 0, // Duration of our animation
      render: function ($container) {
        // Add your CSS animation reversing class
        $container.addClass('is-exiting');

        // Restart your animation
        smoothState.restartCSSAnimations();
      }
    },

    onProgress: {
    // How long this animation takes
    duration: 0,
    // A function that dictates the animations that take place
    render: function ($container) {
            setTimeout(function() { 
                    $container.addClass('is-loading');

                    $('#progressBar').append('<div id="bar"></div>');   
                    var progress = '100%';

                    $('#bar').animate({
                        width: progress
                    }, 400);
    }, 500);
    }
    },

    onReady: {
      duration: 0,
      render: function ($container, $newContent) {
        $container.removeClass('is-loading is-exiting');
        // Inject the new content
        $container.html($newContent);
      },
    },

    onAfter: function() {
            navbarAnimate();
            closeMenu();
            ImageSliders();
            initPhotoSwipeFromDOM('.gallery');
            ImageOverlay(); 
    }
  },


  smoothState = $('#main').smoothState(options).data('smoothState');
});

Just a hint:

you add is-loading, 500ms after the loading process started. So may it be possible that onReady gets fired before your 500ms timeout? And therefore is-loading will be added as class again, after your removeClass call?

tl;dr: the problem is most likely the timeout here

setTimeout(function() { 
  $container.addClass('is-loading');

  $('#progressBar').append('<div id="bar"></div>');   
  var progress = '100%';

  $('#bar').animate({
    width: progress
  }, 400);
}, 500);