When Langfuse is used for tracing (instead of Langsmith), the usage of NeMo-Guardrails in a Langchain chain completely breaks the tracing functionality.

The reason seems to be, that the langchain runnable is not called with the runnable config, which defines callbacks for langchain.
So the LLM runnable that is wrapped in the RunnableRails object is missing the runnable config, and as such the callbacks configured there won't be called and as such the tracing isn't invoked.