Long loading times (or not even loading) with jQiery $.ajax on mobile Safari

I'm working on a web app completely made in JS (using jQery) and HTML.

I discovered a problem with $.ajax and / or $.get calls which do not load or take veeery long to load.

$.ajax({

      dataType: 'jsonp',

      jsonp: 'callBack',

      url: 'http://mmsrv.local/character/userb',

      success: function(ret)

               {

                  $('.charName').text(ret.data.name);

                  $('.charLevel').text(ret.data.level);

                  $('.charExp').text(ret.data.exp);

               }

 });

This is my code to load jsonp. At first I thought it's a problem with unsupported jsonp. But even the following code does not work

$.get({

    url: 'http://localhost/',

    success: function(data) {

        alert(data);

    }

});

The 2nd snippet works perfectly on desktop browser, but not on Mobile Safari. The first one loads well in Desktop browser but goes into a "loading-loop" when visited on Mobile Safari.

Any ideas, why this happens? I saw some others with similiar problems, but it looks like they have other causes.