My app is showing blank white screen when i come back to it

I have this states

    $stateProvider                            
    .state('signup', {
        url : '/signup',
        templateUrl: 'templates/signup/signup.html',
        controller : 'SignupController'               
    });

    $stateProvider
    .state('app', {
        url : '/app',
        abstract : true,
        templateUrl: 'templates/leftmenu.html',
        controller: 'GlobalLeftMenuController'                
    })
    .state('app.home', {
        url: '/home',
        views: {
            'app': {
                templateUrl: 'templates/app-home/templates/home.html',
                controller: 'AppHomeController'                           
            }
        }
    })
    .state('app.contacts', {
        url: '/contacts',
        params: {'params': null},
        views: {
            'app': {
                templateUrl: 'templates/messages/contacts.html',
                controller: 'ContactController'                           
            }
        }
    })

When i come to app.home and press back button app get closed. When i come back i got a blank white screen with no error shown in console. I am simple close the app by pressing middle button it works fine when i come back to app.

Platform:

Ionic1
Android Lollipop

maybe its because the app doesn’t know what state to be routed, then it shows blank, try to use this

  $urlRouterProvider.otherwise('/home');

then it will always go to /home when there is no url matched, put it after the last of your state definition

i added that also but still no luck