[Python] Intermittent None responses from GEMINI-2.5 models (ADK)

I'm getting None responses from the ADK when using the GEMINI-2.5 models, although gemini-2.0-flash works as expected.

• When calling the ADK, gemini-2.5-pro and gemini-2.5-flash intermittently return None (not every call, but frequently).
• I configured max_output_tokens (using a long/integer value) and lowered the thinking budget, but the None responses persist.
• Occasionally the gemini-2.5-pro run yields a MALFORMED_FUNCTION_CALL error and returns None.
• using adk(agent development kit) no vertex.

Library i used:

• google-genai==1.11.0
• google-adk==0.2.0
• python

root_agent = LlmAgent(
name=name.replace(" ", "_"),
model=model,
description=description,
instruction=final_root_agent_instruction,
tools=root_agent_tools,
generate_content_config=types.GenerateContentConfig(
temperature=1.0,
max_output_tokens=1000000))


One of the issue response:

LLM Response:
-----------------------------------------------------------
Text:
None
-----------------------------------------------------------
Function calls:

-----------------------------------------------------------
Raw response:
{"candidates":[{"finish_reason":"MALFORMED_FUNCTION_CALL","index":0}],"model_version":"gemini-2.5-pro","usage_metadata":{"prompt_token_count":502795,"prompt_tokens_details":[{"modality":"TEXT","token_count":502795}],"total_token_count":502795},"automatic_function_calling_history":[]}
-----------------------------------------------------------

2025-08-13 16:29:17,954 - mlalgo.utils.logger - INFO - [Event] Author: Sales_Agent, Type: Event, Final: True, Content: None
2025-08-13 16:29:17,954 - mlalgo.utils.logger - ERROR - Unexpected loop termination - no retry conditions met


I haven't been able to identify the root cause of the intermittent None responses.

Does anyone know the root cause or anyone faced this issue before?

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