現在、Djangoフレームワークを使ってserverを立ち上げています。
ところが、昨日から次のエラーが出てしまうようになりました。

File "/usr/local/lib/python3.6/site-packages/redis/_compat.py", line 123, in iteritems
    return iter(x.items())
AttributeError: 'float' object has no attribute 'items'

一体何が問題でどうしたら解決できるのかわかりません。
対応方法がわかる方、あるいは想像できる方、ご教示ください。
よろしくお願いします。

環境は、次のとおりです。
Python:3.6
Django:2.0.1
redis:2.0

ログの全部はこちらになります。

********@ubuntu:~/********/abcdefghijk$ docker logs -f *********
/usr/local/lib/python3.6/site-packages/celery/platforms.py:796: RuntimeWarning: You're running the worker with superuser privileges: this is
absolutely not recommended!

Please specify a different user using the --uid option.

User information: uid=0 euid=0 gid=0 egid=0

  uid=uid, euid=euid, gid=gid, egid=egid,
[2018-12-06 18:52:48,932: CRITICAL/MainProcess] Unrecoverable error: AttributeError("'float' object has no attribute 'items'",)
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/celery/worker/worker.py", line 205, in start
    self.blueprint.start(self)
  File "/usr/local/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
    step.start(parent)
  File "/usr/local/lib/python3.6/site-packages/celery/bootsteps.py", line 369, in start
    return self.obj.start()
  File "/usr/local/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 322, in start
    blueprint.start(self)
  File "/usr/local/lib/python3.6/site-packages/celery/bootsteps.py", line 119, in start
    step.start(parent)
  File "/usr/local/lib/python3.6/site-packages/celery/worker/consumer/consumer.py", line 598, in start
    c.loop(*c.loop_args())
  File "/usr/local/lib/python3.6/site-packages/celery/worker/loops.py", line 91, in asynloop
    next(loop)
  File "/usr/local/lib/python3.6/site-packages/kombu/asynchronous/hub.py", line 354, in create_loop
    cb(*cbargs)
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/redis.py", line 1040, in on_readable
    self.cycle.on_readable(fileno)
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/redis.py", line 337, in on_readable
    chan.handlers[type]()
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/redis.py", line 724, in _brpop_read
    self.connection._deliver(loads(bytes_to_str(item)), dest)
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 983, in _deliver
    callback(message)
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/virtual/base.py", line 632, in _callback
    self.qos.append(message, message.delivery_tag)
  File "/usr/local/lib/python3.6/site-packages/kombu/transport/redis.py", line 149, in append
    pipe.zadd(self.unacked_index_key, time(), delivery_tag) \
  File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 2263, in zadd
    for pair in iteritems(mapping):
  File "/usr/local/lib/python3.6/site-packages/redis/_compat.py", line 123, in iteritems
    return iter(x.items())
AttributeError: 'float' object has no attribute 'items'

 -------------- celery@92783ffb867f v4.2.0rc4 (windowlicker)
---- **** ----- 
---  **  * -- Linux-4.4.0-112-generic-x86_64-with-debian-9.4 2018-12-06 18:34:29
--  - *** --- 
- ** ---------- [config]
- ** ---------- .> app:         ********:0x7f85fb0d56d8
- ** ---------- .> transport:   redis://redis:6379/0
- ** ---------- .> results:     
- ** ---  --- .> concurrency: 4 (prefork)
-- ******* ---- .> task events: OFF (enable -E to monitor tasks in this worker)
--- ***** ----- 
 -------------- [queues]
                .> default          exchange=default(direct) key=default