Propel Bug Leaderboard: September 2025
Propel Bug Leaderboard
This a ranking of the most frequent bugs found across codebases. The data is derived from the PR comments made by Propel's AI Code Review Agent. Use this snapshot to steer playbooks toward the issues slowing teams down right now.
Top Category
Data Integrity & Migration
19.8%
Insight: Data Integrity & Migration dominated this month. Teams kept running into Schema Change Without Migration, Upsert / Dedupe Logic Bug, and Data Validation / Consistency incidents—clear signs that migration playbooks need tighter guardrails before rollouts.
Top Subcategory
Null or Undefined Guard Missing
Validation & Null Safety
11.6%
Insight: Null or Undefined Guard Missing issues continue to slip through PRs, signaling it's time to invest in automated null-safety linting and stricter guard coverage before merge.
Top Bug Categories in
Aggregated by parent category (including general buckets) so you can see where incident volume is concentrated.
| Rank | Category | Frequency Percentage |
|---|---|---|
| 1 | Data Integrity & Migration | 19.8% |
| 2 | Validation & Null Safety | 16.3% |
| 3 | External Contract Mismatch | 11.7% |
Data Integrity & Migration
Validation & Null Safety
External Contract Mismatch
Top Bug Subcategories in
The ten bug patterns most frequently identified by Propel—general buckets removed so you can focus on actionable fixes.
| Rank | Subcategory | Category | Frequency Percentage |
|---|---|---|---|
| 1 | Null or Undefined Guard Missing | Validation & Null Safety | 11.6% |
| 2 | Authentication / Session Hardening | Security & Access Control | 6.8% |
| 3 | Async Race Condition | State & Concurrency | 6.1% |
| 4 | Integration Field Mapping Mismatch | External Contract Mismatch | 5.3% |
| 5 | Schema Change Without Migration | Data Integrity & Migration | 4.3% |
| 6 | Type / Coercion Error | Validation & Null Safety | 3.8% |
| 7 | Upsert / Dedupe Logic Bug | Data Integrity & Migration | 3.3% |
| 8 | Missing Authorization Checks | Security & Access Control | 3.2% |
| 9 | Data Validation / Consistency | Data Integrity & Migration | 2.9% |
| 10 | Missing Error Handling | Error Handling & Resilience | 2.4% |
Subcategory
Null or Undefined Guard Missing
Category
Validation & Null Safety
Subcategory
Authentication / Session Hardening
Category
Security & Access Control
Subcategory
Async Race Condition
Category
State & Concurrency
Subcategory
Integration Field Mapping Mismatch
Category
External Contract Mismatch
Subcategory
Schema Change Without Migration
Category
Data Integrity & Migration
Subcategory
Type / Coercion Error
Category
Validation & Null Safety
Subcategory
Upsert / Dedupe Logic Bug
Category
Data Integrity & Migration
Subcategory
Data Validation / Consistency
Category
Data Integrity & Migration
Subcategory
Missing Error Handling
Category
Error Handling & Resilience
What To Do With These Insights
September’s bug patterns show that the biggest slowdowns come from a handful of recurring issues. With Propel Code AI, these aren’t surprises. They’re caught in review, before they pile up.
The result: fewer repeat mistakes, faster delivery, and more focus on meaningful work.
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