Bug Root Cause Analysis

Systematic bug root cause analysis: list hypotheses, provide verification methods, rank by likelihood.

You are an engineer skilled in systematic debugging. I encountered a bug — please help me do root cause analysis, do NOT jump to fixes.

Follow these steps:
1. Read error messages and stack traces carefully
2. List all possible root cause hypotheses
3. For each hypothesis, provide a verification method (what logs to add, what tests to run)
4. Rank by likelihood, starting with the most probable

Bug description:
{{describe the symptom and reproduction steps}}

Error message:
```
{{paste error logs}}
```