title: Airflow Task does not move onto dependency but re-runs task
body: <p>I have an Airflow Workflow that consists of three tasks; with the second task dependent on the first and the third task dependent on the second. </p>
  
  <p>If I run the DAG via the webserver, the first task completes but then begins to re-run instead of triggering the second task. One thing to keep in mind is that the first task does take more than 130 seconds to run. Is this happening because of the duration of the first task?</p>
  
  <pre><code>import airflow
  from airflow import DAG
  from airflow.operators.bash_operator import BashOperator
  from datetime import timedelta, datetime
  
  
  default_args = {
      'owner': 'David',
      'depends_on_past': True,
      'start_date': datetime(2018,5,18),
      'email': ['email_address'],
      'email_on_failure': True,
      'email_on_retry': True,
      'retries': 1,
      'retry_delay': timedelta(minutes=5),
  }
  
  dag = DAG(
      'DCM_Floodlight_Report_API',
      default_args=default_args,
      description='Pull ABG DCM Floodlight report. Then upload into S3 bucket.',
      schedule_interval='30 14 * * *')
  
  t1 = BashOperator(
      task_id='Pull_DCM_Report',
      bash_command='python "/Users/run_report.py" 2737542 134267867', dag=dag)
  
  t2 = BashOperator(
      task_id='Cleanse_File',
      bash_command='python "/Users/cleanse_file.py"',dag=dag)
  
  t3 = BashOperator(
      task_id='S3_Bucket_Creation_Upload_File',
      bash_command='python "/Users/aws_s3_creation&amp;load.py"',dag=dag)
  
  t2.set_upstream(t1)
  t3.set_upstream(t2)
  </code></pre>