Think of it this way. You have the pipeline controller which is the 'special' task that manages the logic. Then you have the pipeline steps. Both the controller and the steps need some agent to execute them. So you need an agent to execute the controller and also you need another agent to run the steps themselves.

I would suggest by clicking on 'task_one' and going into full details. My guess it is in 'enqueued' state probably to the 'default' queue.