On Wednesday, September 10, 2025, Polygon, a leading layer-2 scaling network for Ethereum, experienced a temporary disruption in consensus finality due to a bug affecting its Bor and Erigon nodes. The Polygon Foundation confirmed that consensus and finality functions have been restored.
The bug disrupted some Remote Procedure Call (RPC) services, which are essential for relaying information between applications and the blockchain layer, causing access issues for some applications built on the network. While the core blockchain remained operational and continued to produce blocks, several validators and RPC providers had to rewind to the last finalized block and resynchronize to restore accurate network state.
According to Polygon co-founder Sandeep Nailwal, the bug was caused by a "faulty" proposal from a validator, which pushed some of the Bor nodes, used for transaction ordering and block production, onto divergent network forks. The Polygon team rolled out fixes on both Heimdall v0.3.1 and Bor 2.2.11 beta2, purging the milestone from the database. With these fixes in place, nodes are no longer stuck, and checkpoints and milestones are finalizing normally.
The team identified that the bug prevented node progress for certain configurations. Restarting the affected nodes restored functionality for many participants. Engineers collaborated with infrastructure providers to accelerate debugging and restore full service. Polygon emphasized that the disruption did not affect core chain operations.
The situation caused confusion among users when Polygonscan, the network's block explorer, showed no new blocks for more than five hours. A Polygon representative clarified that Polygonscan's nodes halted at a bad milestone produced by Heimdall, the network's consensus engine. Users were redirected to an alternative tracker showing that blocks were still being produced in real time.
Deeper analysis revealed that Heimdall's finality gadget, which usually produces milestones every few seconds, was not creating new milestones. As a result, block finality was delayed until checkpoints were posted on Ethereum. Despite the delay, the chain continued to add blocks without interruption.
At 08:52 UTC, Polygon reported that checkpoint finality was functioning as expected, with confirmations occurring every 15 minutes. The team confirmed via X that a fix had been identified and was being rolled out to validators and service providers.
The incident highlights the challenges of maintaining high throughput and reliability in complex cryptographic protocols that host smart contract functionality, file storage, and cross-chain interoperability. As blockchain protocols become more complex, software bugs may become more frequent, potentially disrupting the on-chain user experience.
