# Polygon PoS Incident Postmortem: Milestone Bug & Hard Fork Resolution Source: https://etherworld.co/2025/09/10/polygon-pos-incident-postmortem-milestone-bug-hard-fork-resolution Kiwi News: https://news.kiwistand.com/stories/Polygon-PoS-Incident-Postmortem-Milestone-Bug-and-Hard-Fork-Resolution?index=0x68c346d7f7293d2ecba819983b74bb974e73505d378c5fa7615774dd2125b42642fac2c8 Submitted by misha on 2025-09-11 UTC, 1 upvote, 0 comments ## Summary Polygon PoS suffered a disruption in which milestone-based fast finality was delayed while Ethereum checkpoint finality stayed active, and the team says transactions remained secure. The incident was traced to a faulty milestone proposal that caused Bor nodes to fork, and it was resolved with Heimdall v0.3.1, a hard fork that removed the faulty milestone, and Bor v2.2.11-beta2, which purged milestone data from local node databases. After these fixes, checkpoints and milestones finalized normally and consensus stability was restored. ## Article Polygon PoS recently experienced a disruption where checkpoint finality on Ethereum remained active, but local fast finality (milestones) was delayed. While transactions were still secure, milestone confirmations faced instability due to a faulty proposal. Polygon engineers acted swiftly to resolve the issue through coordinated fixes on Heimdall & Bor, successfully restoring consensus stability. What Happened Root Cause Analysis Fixes & Recovery Implications & Road Ahead What Happened Earlier yesterday, Polygon PoS validators observed delays in milestone-based fast finality. While Ethereum checkpointing continued normally, milestones lagged, creating temporary instability. This led to forks among Bor nodes and short-term confusion within the network. Milestones serve as a lightweight alternative to checkpoints, offering faster finality before transactions are secured on Ethereum. Before Heimdall v2: 60–90 seconds After Heimdall v2: 3–6 seconds Each validator independently proposes milestones, enabling efficiency but also raising complexity in consensus coordination. Root Cause Analysis The incident was traced back to a faulty milestone proposal, which caused Bor nodes to diverge onto separate forks. Since this edge case was not anticipated, the network experienced temporary instability until corrective measures were applied. https://t.co/ulINLtlurVSeptember 10, 2025 Fixes & Recovery Polygon engineers rolled out rapid fixes across both core layers: Heimdall v0.3.1 (Hard Fork): Removed the faulty milestone. Bor v2.2.11-beta2: Purged milestone data from local node databases. Following these updates, checkpoints & milestones finalized normally, and consensus stability was fully restored. Implications & Road Ahead This event underscores the challenges of ambitious upgrades in blockchain networks. Polygon emphasized that such incidents are part of its growing pains, but each strengthens resilience. Polygon PoS has successfully overcome a milestone-related disruption with swift engineering fixes. With finality restored and stability ensured, the network continues to move forward toward scalability. If you find any issues in this blog or notice any missing information, please feel free to reach out at yash@etherworld.co for clarifications or updates. Related Articles Polygon PoS Hard Fork Polygon's L2 Solution How to Use Polygon testnet? Polygon announces to launch zKEVM mainnet beta How Polygon is helping Blockchain Movement in India? Disclaimer: The information contained in this website is for general informational purposes only. The content provided on this website, including articles, blog posts, opinions, & analysis related to blockchain technology & cryptocurrencies, is not intended as financial or investment advice. The website & its content should not be relied upon for making financial decisions. Read full disclaimer & privacy policy. For Press Releases, project updates & guest posts publishing with us, email contact@etherworld.co. Subscribe to EtherWorld YouTube channel for ELI5 content. Share if you like the content. Donate at avarch.eth. You've something to share with the blockchain community, join us on Discord! Follow us on Twitter, Facebook, LinkedIn & Instagram.