UPDATED:  We are on Laserfiche Forms Professional Version 10.4.1.164. I put a field above Action, and it solved my issue BUT only the first time through. When I rejected and received that task back, it didn't solve my issue:

I think it has to do with "on form open", it runs the Field Rules first, and the JavaScript second. In the JS, I clear the Reject value, but because Field Rules runs first, it doesn't know that yet and still sees a Reject. So, I decided to put the show/hide in JS:

$(document).ready(function(){

//Reset "Action" radio buttons and rejectionComments field
  $("#Field67-0").prop("checked", false); //clear reject button
  $("#Field67-1").prop("checked", false); //clear approve button
  $('.rejectionComments textarea').val('');
  $('.rejectionComments').hide();

//Show/Hide Rejection Comments field
  $('.action input').change(function () {
    if ($(this).val() == "Reject")
    {
      $('.rejectionComments').show();
    }
    else
    {
      $('.rejectionComments').hide();
    }
  });
  $(".action input:checked").each(function(){  
    $(this).trigger('change');
  });

});  //close document.ready

Works great, but now I have a new issue. Rejections work great! But when I try to Approve, my "Task Complete" button does nothing.

I'm close! In case you wanted to see my Outflows:

Triggering a change event when you clear the value should trigger the field rule.

I always do .val('').change() to ensure field rules, calculations, etc., are properly updated.