Hey folks! I’m trying to update my codebase from Prefect 2 -> 3, and running into an issue with starting new tasks push work pools on ECS. For a new flow run, the container fails to start successfully, and outputs the following stack trace:

Traceback (most recent call last):
File "/bin/app/lib/python3.12/site-packages/prefect/engine.py", line 37, in <module>
flow_run, flow = load_flow_and_flow_run(flow_run_id=flow_run_id)

File "/bin/app/lib/python3.12/site-packages/prefect/flow_engine.py", line 102, in load_flow_and_flow_run
flow_run = client.read_flow_run(flow_run_id)

File "/bin/app/lib/python3.12/site-packages/prefect/client/orchestration.py", line 3923, in read_flow_run
return FlowRun.model_validate(response.json())

File "/bin/app/lib/python3.12/site-packages/pydantic/main.py", line 596, in model_validate
return cls.__pydantic_validator__.validate_python(

pydantic_core._pydantic_core.ValidationError: 1 validation error for FlowRun
labels
Input should be a valid dictionary [type=dict_type, input_value=None, input_type=NoneType]
For further information visit <https://errors.pydantic.dev/2.9/v/dict_type>

00:46:23.724 | ERROR | prefect.engine - Engine execution of flow run '10b5cda5-a0fa-4ad5-a9fe-b08d89925e17' exited with unexpected exception

How can I go about debugging this issue? I’m using Prefect Cloud + Prefect 3 and it’s hard to figure out what exactly is broken in this chain.

hi @Krishnan Chandra ! hmm this looks like a bug related to a recent change can you try downgrading to 3.1.0 in the meantime?

Yes! I filed an issue on Github with more information: https://github.com/PrefectHQ/prefect/issues/16066

thank you so much! well look into this tomorrow