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Sofia Bennett
Sofia Bennett

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When an AI Misreads a Stack Trace: Lessons from Debugging with Language Models

When the model misreads stack traces

I started treating the model like a junior engineer: feed it a stack trace, ask what likely failed, and iterate. Early on it seemed productive — short cycles, suggested fixes, and quick hypotheses. But I hit a consistent failure mode: the model would assert a confident explanation for an exception while silently misattributing frames or omitting async/callback context that actually mattered.

That mismatch showed up during multi-turn debugging sessions where the conversation assumed persistent context. The model would generate a plausible root cause and then, when probed, double down on the same incorrect frames instead of reconciling earlier clarifications. In those moments I relied on a multi-turn assistant like chat to drive the iteration, and the conversational convenience hid the model’s tendency to lock onto an early, incorrect hypothesis.

How it surfaced in real debugging sessions

On one incident a service returned a null-pointer originating in a utility module, and the model recommended changing the caller code. The stack trace suggested the utility as the failing function, but the actual cause was a race in the caller that only manifested under specific scheduling conditions. The model’s suggestion made the test suite green locally but failed intermittently in production, because it hadn’t accounted for the asynchronous scheduling frame that was absent in the truncated trace snippet.

Part of the problem was how we prepared inputs. A teammate pasted a cropped screenshot of a log and used a quick visual enhancement tool to make the text readable; that improved legibility but introduced OCR artifacts that the model ingested as real tokens. I’ve seen workflows where an image pipeline such as an AI Image Upscaler is used to clarify screenshots, but unless the OCR and transcription are validated, the model works from corrupted evidence and confidently rationalizes the resulting mismatch.

Why the mistake is subtle and easy to miss

The model emits fluent explanations that feel like correct reasoning. That fluency masks that it’s pattern-matching stack frames and exception names rather than executing causal inference. When frames are obfuscated, inlined, or reordered by optimizations, the model fills gaps with the most statistically likely mapping even if it’s wrong. Human readers can be persuaded by a succinct narrative and stop cross-checking assumptions.

Subtle duplications in function names, library wrappers, or generated code make it worse: the model latches onto the nearest human-readable symbol and ignores context such as thread IDs, timestamps, or prior async callbacks. The remedy I settled on was to treat the model’s diagnosis as a draft and then use a verification loop — cross-checking call stacks, reproducing locally, or consulting curated references using tools like deep research to confirm assertions before applying a fix.

How small behaviors compound into larger workflow problems

Individually these misreads are cheap — a wasted 10–15 minute patch or an unnecessary refactor. Over months they erode trust: engineers start applying model suggestions without testing, or they spend time reverting changes the model caused. The real cost is cultural: when a team normalizes fluent but unchecked answers, brittle fixes accumulate and debugging skills atrophy.

Practical mitigations are straightforward: normalize trace hygiene (full, untampered traces), include environmental metadata, require a reproducible test that fails before accepting a model-driven change, and log the provenance of AI suggestions. Treat AI output as a draft hypothesis, not a final verdict, and build simple verification gates into your workflow to catch these subtle failures early.

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