Hey Sam,

Sorry was caught up with my implementation specialist exam.

This is puzzling, the order of tasks shouldn't make any difference, can you please modify the BR as follows -

function executeRule(current, previous /*null when async*/) {

var email_to = [];
var sc_task = new GlideRecord('sc_task');
sc_task.addQuery('request_item',current.sys_id+'');
sc_task.addActiveQuery();                             //eliminates the inactive/closed tasks, optimizes the results
sc_task.query();
while (sc_task.next()){

  gs.log("sam1");
  if (sc_task.assigned_to == "" || sc_task.assigned_to == null){                 //included the null keyword as sometimes the system doesn't compare successfully with ""
                gs.log("sam2 "+sc_task.assignment_group.manager);

                email_to.push(sc_task.assignment_group.manager+'');
  }
  else{                                                                                                                                                                                                 //added an else to optimize the query
              gs.log("sam3 "+sc_task.assigned_to);

              email_to.push(sc_task.assigned_to+'');
  }
}

gs.log("sam4 "+email_to);
gs.eventQueue("sc_req_item.commented.itil", current, email_to.join(), gs.getUserName());

})(current, previous);

I've just tweaked the logs and the email_to.push statement.

Please run all the 4 use cases and share the logs/results:

1. both tasks have assigned to

2. both tasks don't have assigned to

3. task 1 has assigned to & task 2 doesn't

4. task 2 has assigned to & task 1 doesn't