Added a check for syncing the schedule even if nothing is in the schedule.

celery/beat.py

@@ -504,6 +504,8 @@ class Service(object):
                     debug('beat: Waking up %s.',
                           humanize_seconds(interval, prefix='in '))
                     time.sleep(interval)
+                    if self.scheduler.should_sync():
+                        self.scheduler._do_sync()
         except (KeyboardInterrupt, SystemExit):
             self._is_shutdown.set()
         finally: