Django crontab日志：ModuleNotFoundError：没有名为'sslserver'的模块

Question

我在服务器上运行了一个django crontab，如果我看到它的日志，则会出现以下错误。

  File "/usr/local/lib/python3.6/dist-packages/django/apps/registry.py", line 85, in populate
    app_config = AppConfig.create(entry)
  File "/usr/local/lib/python3.6/dist-packages/django/apps/config.py", line 94, in create
    module = import_module(entry)
  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'sslserver'

如果我通过运行python manage.py crontab run手动运行cron，它将运行正常。

我还尝试运行pip install -r requirements.txt，它说依赖关系已经满足。

有什么主意我该如何克服？