On Wednesday, the Beacon Chain, which will bring proof-of-stake (PoS), to Ethereum (ETH), underwent a seven-block reorganization.

Reorgs can be caused by a malicious attack by a miner with high resource or by network failures such as a bug. This temporarily creates a duplicate of the blockchain, which could pose a high-level security threat.

According to data from Beacon Scan, seven blocks numbered 3,887.075 to 3887.081 were removed from the Beacon Chain on May 25th. Martin Koppelmann (CEO and cofounder of Gnosis, decentralized finance service provider DeFi), said that the reorganization is the longest in years.

Koppelmann observed that this “shows the need to reconsider the current attestation strategy for nodes in order to hopefully create a more stable chain!” (Proposals are already available). This means there is still much work to do before the Merge, which is expected to take place later in the year.

Preston Van Loon, a core Ethereum developer, speculated that the reorg was caused by “the implementation of Proposer Boostfork”, a term that describes a process in which certain proposers are given priority in selecting the next block in a blockchain.

Van Loon stated that he suspects the problem is due to Proposer Boost’s inadvertent rollout to the network. This reorganization is not indicative of a flawed fork selection, but rather a non-trivial division of out of date client applications.

Vitalik Buterin, cofounder of Ethereum, called this theory “good hypothesis” and suggested that it might have been due to “boosted vs. unboosted nodes in network and the timing a really late arriving block.”

According to the developer, the coincidence was only 0.00025% likely given the circumstances.