TypeError: 'Machine' object is not iterable

hi guys:
my maas version is 2.6.2
i am control maas by api to deploy a machine.
when i call the deploy api , it will raise error:

2021-10-27 11:21:49 maasserver: [error] ################################ Exception: 'Machine' object is not iterable ################################
2021-10-27 11:21:49 maasserver: [error] Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 277, in view_atomic_with_post_commit_savepoint
    return view_atomic(*args, **kwargs)
  File "/usr/lib/python3.6/contextlib.py", line 52, in inner
    return func(*args, **kwds)
  File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 70, in __call__
    response = upcall(request, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/views/decorators/vary.py", line 21, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/piston3/resource.py", line 229, in __call__
    else: stream = srl.render(request)
  File "/usr/lib/python3/dist-packages/piston3/emitters.py", line 464, in render
    response = serializers.serialize(format, self.data, indent=True)
  File "/usr/lib/python3/dist-packages/django/core/serializers/__init__.py", line 129, in serialize
    s.serialize(queryset, **options)
  File "/usr/lib/python3/dist-packages/django/core/serializers/base.py", line 80, in serialize
    for count, obj in enumerate(queryset, start=1):
TypeError: 'Machine' object is not iterable

2021-10-27 11:21:49 regiond: [info] 127.0.0.1 POST /MAAS/api/2.0/machines/gbcq8k/?op=deploy HTTP/1.1 --> 500 INTERNAL_SERVER_ERROR (referrer: -; agent: python-requests/2.25.1)

i have to restart maas service to workaround。
but it will happen again sometimes。。。。
it just happen occasionly .

with greate appreciate.
my emal is 990967768@qq.com

This may be a bug in 2.6.2; unfortunately, MAAS version 2.6 is no longer supported. Please upgrade to MAAS 3.0 or greater and attempt your operation again, then report back if you are still experiencing the issue.

Closing this post for now.