File variable are set to null when go back to previous task

The process flow to simulate the issue

  1. Task1 with an download element¹ to be showed if there is a file;
  2. Task2 with an upload input file element² and an approve or not (approved) variable; NOTE THAT I CAN DOWNLOAD THE FILE AT THE NEXT TASK (e.g. task03) BUT NOT AT PREVIOUS TASK
  3. approved = false;
  4. Task1 show the download element¹ with the file_task2 variable; HERE THE ISSUE

¹<a id="showDownloadFileTask2" cam-file-download="file_task2"></a>

²input element at embedded formTask2:

    <input type="file"
            cam-variable-name="file_task2"
            cam-variable-type="File"/>

Explaining the issue more deeper

I used the console.log from cam-script at embedded form

  <script cam-script type="text/form-script">
        $scope.userName = '';
        var variableManager = camForm.variableManager;

        camForm.on('form-loaded', function() {
              try {
                variableManager.fetchVariable('file_task2');
              } 
              catch (err) {
                console.log(err);
              }
        });

       camForm.on('variables-fetched', function() {
          console.log("file = "+variableManager.variableValue('file_task2')); //file = null
          if(processAndGetVariable('file_etp_conformidadeETP') == null) {
              document.getElementById('showDownloadFileTask2').style = "display: none;";
          }
        });
  </script>

How can I access that variable from task1 form ?

Input/Output ?
Create the variable at start process?
What else can I do?
Maybe create the file variable in task2 using camunda modeler ?