When the scroll bar appears in the Gantt chart area, you can no longer drag to create a new task without parent

hello,When there are too many tasks in Gantt chart, scroll bar will appear,Created tasks are all subtasks

I think it is expected because to create a new task that doesn’t have parents, you need to have an empty space.
The easiest way to make it work that way is to use a placeholder task that will add an empty row at the bottom. However, if you draw a line there, the tasks will be added as subtasks of the placeholder task. So, you need to change their parent:

gantt.config.placeholder_task = true;

gantt.attachEvent("onBeforeLightbox", function(id) {
    var task = gantt.getTask(id);
  	if (task.parent) {
      var parent = gantt.getTask(task.parent)
      if(parent.type == 'placeholder'){
        task.parent = 0;
    return true;

Here is an example of how it works:

According to your example, I have implemented this function. Thank you.