Smothe fadeIn() animation

I got an issue with my fadeIn animation which wont work properly. Instead it appears instantly without any animation at all?

    function createABRN(url){

       formSerial2 = $  ('#baseForm').serialize();
       $  ("input[name='ipreis']").val($  selPositionVals[1]);

       $  .ajax({
            type: "POST",
            url: url,
            data: formSerial2,
            success: function(msg){

              $  (".alert").html(msg);
              $  (".alert").append($  ($  delBillLink));
              createPositions();

              $  ('input[name="aufbest"]').hide();
              $  ('input[name="iweiter"]').hide();

              $  ('.position').fadeIn(); //<-- no animation, just jumps in?
            }
        });     

}

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