Polygon PoS Incident Postmortem: Milestone Bug & Hard Fork Resolution

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.