Unexpected empty input/output fields in traces when using LangFuse

[ArtikMastik]

Describe your question

Hi,
I’m using LangFuse and noticing that some of my trace/observation entries show empty input/output fields, even though the underlying LLM calls definitely have content.

I saw the FAQ entry here:
https://langfuse.com/faq/all/empty-trace-input-and-output

but I don’t fully see how it applies to my case or why these specific observations end up with empty values.

My setup:

Using the Langfuse callback handler

Inputs and outputs are present in the actual LLM responses

Only some lines are missing the data, not all

I’m not manually removing or redacting anything

Could someone explain why this happens or guide me on how to debug it properly?
Thanks!

Langfuse Cloud or Self-Hosted?

Self-Hosted

If Self-Hosted

v3.118.0

If Langfuse Cloud

No response

SDK and integration versions

No response

Pre-Submission Checklist

• I have checked for existing issues/discussions and consulted Langfuse AI.

[jannikmaierhoefer]

Thanks @ArtikMastik, can you observe a pattern for the traces where this is the case, or does it seem to be random?

[ArtikMastik]

Thanks for the follow-up.

I looked again and noticed something additional:
In the traces where the input and output are empty, the metadata field is also empty.
You can see it clearly in the middle line of this screenshot (the other traces have full metadata):

(attached screenshot)

So the pattern seems to be:

• Input: empty
• Output: empty
• Metadata: empty
• But the LLM call itself definitely had content
• And in the same execution flow, other traces have full input/output/metadata

This makes it feel less random and more like those specific observations were never fully populated by the callback, even though the surrounding ones were.

Let me know what else I should check.

Thanks!

[jannikmaierhoefer]

Thanks @ArtikMastik, if I remember correctly, this issue has been fixed in a later release. Could you upgrade to the latest Langfuse version and try again?

[ArtikMastik]

It might take a bit of time on our side to upgrade and validate everything, but we’ll update to the latest version and test it.
I’ll report back once we have results.

Thank you @jannikmaierhoefer!