我有一个遗留的Django项目（django-1.1.29）和一些pytest测试（pytest-4.3.0），都在Docker中运行。数据库是PostgreSQL 10，是应用程序所依赖的docker-compose服务。Python版本是2.7.18。
最近，测试开始失败，出现了一个奇怪的错误：
InternalError: variable not found in subplan target list .
只有当我计算某个模型的对象数量时才会出现错误，例如。Problem.objects.count()。该指令被转换为以下查询
Django的(0.000) SELECT COUNT(*) AS "__count" FROM "problems_problem"; args=()。
整个日志在这里：

self = <integration_tests.project_name.subjects.test_views.test_theme_problem_view_set.TestThemeProblemViewSet object at 0x7f01faccbe50>
jclient = <project_name.common.test_utils.json_client.JSONClient object at 0x7f01fadb8ed0>

    def test_all_is_ok(self, jclient, subject_model, content_manager):
        url, data = self._main_prepare(jclient, subject_model, content_manager)
        response = jclient.post_json(url, data[0])
        assert response.status_code == 201
>       assert Problem.objects.count() == 1

integration_tests/project_name/subjects/test_views/test_theme_problem_view_set.py:86: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py:85: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
/usr/local/lib/python2.7/dist-packages/django/db/models/query.py:364: in count
    return self.query.get_count(using=self.db)
/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:499: in get_count
    number = obj.get_aggregation(using, ['__count'])['__count']
/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py:480: in get_aggregation
    result = compiler.execute_sql(SINGLE)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <django.db.models.sql.compiler.SQLCompiler object at 0x7f01faee3a50>
result_type = 'single', chunked_fetch = False

    def execute_sql(self, result_type=MULTI, chunked_fetch=False):
        """
        Run the query against the database and returns the result(s). The
        return value is a single data item if result_type is SINGLE, or an
        iterator over the results if the result_type is MULTI.
    
        result_type is either MULTI (use fetchmany() to retrieve all rows),
        SINGLE (only retrieve a single row), or None. In this last case, the
        cursor is returned if any query is executed, since it's used by
        subclasses such as InsertQuery). It's possible, however, that no query
        is needed, as the filters describe an empty set. In that case, None is
        returned, to avoid any unnecessary database interaction.
        """
        if not result_type:
            result_type = NO_RESULTS
        try:
            sql, params = self.as_sql()
            if not sql:
                raise EmptyResultSet
        except EmptyResultSet:
            if result_type == MULTI:
                return iter([])
            else:
                return
        if chunked_fetch:
            cursor = self.connection.chunked_cursor()
        else:
            cursor = self.connection.cursor()
        try:
            cursor.execute(sql, params)
        except Exception as original_exception:
            try:
                # Might fail for server-side cursors (e.g. connection closed)
                cursor.close()
            except Exception:
                # Ignore clean up errors and raise the original error instead.
                # Python 2 doesn't chain exceptions. Remove this error
                # silencing when dropping Python 2 compatibility.
                pass
>           raise original_exception
E           InternalError: variable not found in subplan target list

/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py:899: InternalError

如果有人能帮我解决这个问题，或者至少给予出一些提示，在哪里找到原因，我真的会很感激。
以下是我到目前为止尝试做的事情，但这些都没有帮助：

• 使用不同版本的PostgreSQL（10，11，12，13）
• 禁用服务器端游标