Three Sui mainnet halts in 48 hours traced to an upgrade bug by developers

A new feature shipped in Sui’s v1.72 release exposed an edge case in the Layer-1 blockchain’s gas-charging logic that halted mainnet three separate times across May 28 and May 29, with each fix either triggering or exposing the next failure, the Sui Foundation said in a post-mortem published Sunday.

The first outage began at roughly 7 a.m. PT on Thursday and lasted close to seven hours.

According to the foundation, it stemmed from a rare issue in how the network charged gas for transactions paying with a mix of the new address-balance feature and traditional coin objects. The bug caused validators to crash with an underflow error when a transaction was canceled for insufficient funds, but the gas-smashing routine still tried to spend those same funds.

Think of a coin object as a digital banknote. A user’s SUI balance isn’t a single number — it’s a stack of distinct “notes,” each with its own ID, that can be moved or combined. The wallet might hold three coin objects worth 60, 30, and 10 SUI rather than a single 100-SUI balance. To pay for something, the network combines the notes it needs.

Validators are computers (and the operators behind them) that run the network by processing transactions, voting on which ones are valid, and keeping the chain alive.

The core team brought the network back up around 1:30 p.m. PT with what it called an “interim fix” that addressed the most common version of the bug but carried “a known issue with a low probability of causing a halt.” The team accepted that risk to restore the mainnet quickly while a more robust fix was developed.

The known risk materialized the next morning. A second outage began around 5 a.m. PT on Friday, when a transaction triggered a masked variant of the same bug, in which the insufficient-funds error was overridden by another cancellation reason, bypassing the interim patch. The core team finished a more robust fix, and validators adopted it by about 9:40 a.m. PT.

The third halt was a knock-on from the second. When validators restarted to install the robust fix, validator participation in the protocol that bootstraps the network’s on-chain randomness fell below the required threshold, and randomness disabled itself as designed.

(On-chain randomness is a protocol the network uses to produce a number nobody can predict or fake, even though every validator has to agree on the same value. Apps that depend on chance — lotteries, certain games, random NFT mints — can’t run without it.)

A latent bug then failed to persist that disabled state to disk, leaving validators unaware on the next restart that randomness had been turned off. The next epoch change stalled for close to six hours as randomness-dependent transactions piled up in a paused queue.

No user funds were at risk during any of the outages, and no committed transactions were reverted, the foundation said.

SUI dropped roughly 8% during the cascade to a low of $0.90 and was trading near $0.90 on Monday, leaving the token down about 19% on the week, per CoinDesk data.

The events represent Sui’s third major reliability incident since its 2023 mainnet launch, following a two-hour transaction scheduling bug in November 2024 and a six-hour consensus divergence in January 2026.