
When Errors Become Narratives: A Longitudinal Taxonomy of Silent Failures in a Production LLM Agent Runtime
This longitudinal study of a production LLM agent system reveals a critical pattern: silent failures where error signals never reach humans in actionable form, occurring 28+ times over 8 weeks despite extensive testing. The five-class taxonomy of failure modes is immediately actionable for anyone building agent systems, with 'chained hallucination and fabrication' being uniquely dangerous to LLM systems. This is must-read research for understanding how LLM agents fail differently from traditional software.
Takeaways3
- Silent failures where errors don't surface to humans are a critical failure mode unique to LLM agent systems.
- Traditional testing approaches (4,286 unit tests, 827 governance checks) don't prevent these failure patterns.
- Chained hallucination represents the most dangerous failure class, where systems confidently fabricate plausible but wrong information.










