Ошибка 'NoneType' object has no attribute 'twophase в sqlalchemy

В ходе выполнения этой функции иногда получаю ошибку: 'NoneType' object has no attribute 'twophase в sqlalchemy. Очень мало информации в интернете, подскажите, куда копать? БД - PostgreSQL 13.3 Драйвер - asyncpg

    async def update_category_in_db(self, id_okolo: str, body: dict):
    await async_db_session.init()
    try:
        query = select(Category).where(Category.id_ras == body['categories'][0]['article']).join(Partner).where(
            Partner.code_okolo == body['partner'])
        result = await async_db_session.execute(query)
        product = result.scalars().first()
        product.id_okolo = id_okolo
        await async_db_session.commit()
        return True
    except Exception as e:
        logger.error(
            f'ERROR ошибка sql запроса {e} в файле {os.path.abspath(__file__)} метод: update_category_in_db')
    finally:
        await async_db_session.conn_close()

Вот трэйсбэк:

   Traceback (most recent call last):
  File "/src/okolo_server/nomenclature.py", line 75, in update_category_in_db
    result = await async_db_session.execute(query)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/ext/asyncio/session.py", line 145, in execute
    **kw
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 122, in greenlet_spawn
    result = context.switch(value)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1676, in execute
    conn = self._connection_for_bind(bind, close_with_result=True)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1527, in _connection_for_bind
    engine, execution_options
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 754, in _connection_for_bind
    if self.session.twophase and self._parent is None:
AttributeError: 'NoneType' object has no attribute 'twophase'

Так выглядит мой объект сессии:

class AsyncDatabaseSession(object):
    def __init__(self):
        self._session = None
        self._engine = None

    def __getattr__(self, name):
        return getattr(self._session, name)

    async def init(self):
        self._engine = create_async_engine(
            'postgresql+asyncpg://{user}:{password}@{host}:{port}/{db}'.format(
                user=os.getenv('POSTGRES_USER'),
                password=os.getenv('POSTGRES_PASSWORD'),
                host=os.getenv('POSTGRES_HOST'),
                port=os.getenv('POSTGRES_PORT'),
                db=os.getenv('POSTGRES_DB')
            )
        )
        self._session = sessionmaker(
            self._engine, expire_on_commit=False, class_=AsyncSession,
        )()

    async def conn_close(self):
        """Закрытие сессии"""
        await self._session.close()

    async def create_all(self):
        async with self._engine.begin() as conn:
            await conn.run_sync(Base.metadata.create_all)


async_db_session = AsyncDatabaseSession()