I think that every row in the Gantt chart is based on a single entity, in this case ActiveSeparate and JtTask. Unfortunately the assigned resource is not available on the task, but rather on the assignment. So could either try to add assignment as another level below task (I never tried this kind of modification TBH and it may also have a performance impact), or use a BPA to populate a custom field on the task whenever an assignment is created (assuming the simple case that there is one assignment per task only).