# Some percentage of an experiment run randomly fail, some also randomly dont get "feedback"

**URL:** <https://forum.langchain.com/t/some-percentage-of-an-experiment-run-randomly-fail-some-also-randomly-dont-get-feedback/570>\
**Category:** Observability & Evals\
**Created:** [July 19, 2025, 5:50pm UTC](https://forum.langchain.com/t/some-percentage-of-an-experiment-run-randomly-fail-some-also-randomly-dont-get-feedback/570 "2025-07-19T17:50:50Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![alonp99](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/alonp99/32/266_2.png) [@alonp99](https://forum.langchain.com/u/alonp99)\
**Post date:** [July 19, 2025, 5:50pm UTC](https://forum.langchain.com/t/some-percentage-of-an-experiment-run-randomly-fail-some-also-randomly-dont-get-feedback/570/1 "2025-07-19T17:50:50Z")

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The error presented on langsmith UI, run output gets:

“TypeError(”‘MockValSer’ object cannot be converted to ‘SchemaSerializer’")Traceback (most recent call last):

File “/usr/local/lib/python3.11/site-packages/langchain\_core/runnables/base.py”, line 909, in ainvoke

File “/usr/local/lib/python3.11/site-packages/langchain\_core/language\_models/chat\_models.py”, line 400, in ainvoke

File “/usr/local/lib/python3.11/site-packages/langchain\_core/language\_models/chat\_models.py”, line 974, in agenerate\_prompt

File “/usr/local/lib/python3.11/site-packages/langchain\_core/language\_models/chat\_models.py”, line 932, in agenerate

File “/usr/local/lib/python3.11/site-packages/langchain\_core/language\_models/chat\_models.py”, line 1100, in \_agenerate\_with\_cache

File “/usr/local/lib/python3.11/site-packages/langchain\_openai/chat\_models/base.py”, line 1355, in \_agenerate

File “/usr/local/lib/python3.11/site-packages/langchain\_openai/chat\_models/base.py”, line 3618, in \_construct\_lc\_result\_from\_responses\_api

File “/usr/local/lib/python3.11/site-packages/pydantic/main.py”, line 426, in model\_dump

TypeError: ‘MockValSer’ object cannot be converted to ‘SchemaSerializer’"

and on the feedback column regardless of what happend in the output i see random occurrences of : “No feedback”

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<div class="post-metadata">

**Author:** ![alonp99](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/alonp99/32/266_2.png) [@alonp99](https://forum.langchain.com/u/alonp99)\
**Post date:** [July 21, 2025, 4:34am UTC](https://forum.langchain.com/t/some-percentage-of-an-experiment-run-randomly-fail-some-also-randomly-dont-get-feedback/570/2 "2025-07-21T04:34:09Z")

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It happens only with o4-mini