end session error

[lukeolson]

The process failed and reported the following error:

Traceback (most recent call last):
  File "/home/andreas/my-relate-env3/lib/python3.7/site-packages/celery/app/trace.py", line 382, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/home/andreas/my-relate-env3/lib/python3.7/site-packages/celery/app/trace.py", line 641, in __protected_call__
    return self.run(*args, **kwargs)
  File "/home/andreas/relate/course/tasks.py", line 58, in expire_in_progress_sessions
    past_due_only=past_due_only):
  File "/home/andreas/relate/course/flow.py", line 1284, in expire_flow_session_standalone
    past_due_only=past_due_only)
  File "/home/andreas/relate/course/flow.py", line 1067, in expire_flow_session
    now_datetime=now_datetime, respect_preview=False)
  File "/home/andreas/relate/relate/utils.py", line 334, in wrapper
    serializable=self.serializable)
  File "/home/andreas/relate/relate/utils.py", line 310, in retry_transaction
    return f(*args, **kwargs)
  File "/home/andreas/relate/course/flow.py", line 979, in finish_flow_session
    respect_preview=respect_preview)
  File "/usr/lib/python3.7/contextlib.py", line 74, in inner
    return func(*args, **kwds)
  File "/home/andreas/relate/course/flow.py", line 931, in grade_page_visits
    page_data = flow_session.page_data.get(page_ordinal=i)
  File "/home/andreas/my-relate-env3/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/andreas/my-relate-env3/lib/python3.7/site-packages/django/db/models/query.py", line 412, in get
    (self.model._meta.object_name, num)
course.models.FlowPageData.MultipleObjectsReturned: get() returned more than one FlowPageData -- it returned 2!