title: Celery cancels itself
body: <p>When I try to run a worker:</p>
  
  <p><code>celery -A celery_conf --loglevel=debug worker -Q celery -c 1</code></p>
  
  <p>It seems to start, but then it "cancel"s</p>
  
  <pre><code>[2018-08-07 16:25:16,132: INFO/MainProcess] Connected to redis://server:6379/1
  [2018-08-07 16:25:23,984: DEBUG/MainProcess] Canceling task consumer...
  [2018-08-07 16:25:24,993: DEBUG/MainProcess] Canceling task consumer...
  [2018-08-07 16:25:24,993: DEBUG/MainProcess] Closing consumer channel...
  [2018-08-07 16:25:24,993: WARNING/MainProcess] Restoring 1 unacknowledged message(s)
  [2018-08-07 16:25:24,996: DEBUG/MainProcess] removing tasks from inqueue until task handler finished
  </code></pre>
  
  <p>Any idea how to begin debugging? I already have the loglevel to DEBUG.</p>
  
  <ul>
  <li>Celery version: 4.2.1 (also tested on master)</li>
  <li>Python version: 3.6.6</li>
  <li>Using a Redis Broker</li>
  </ul>