More than $600 million in trades occurred on Polymarket after the outcomes of certain election contracts were already decided.
The activity centered on markets tied to elections in Ethiopia and Romania, according to a report from Wired.
Trading continued at high volumes even after the results of those races had become clear.
This pattern raised concerns among observers who monitor prediction markets for signs of abuse.
One expert described the activity as an obvious form of volume manipulation.
Polymarket is a decentralized platform where users bet on real-world events using cryptocurrency.
Such markets are designed to reflect the probability of future outcomes, not settled ones.
Trades placed after an event concludes can distort volume statistics and mislead users.
The report did not specify who was behind the trades or whether they profited.
Polymarket has not publicly commented on the findings at the time of the report.
Prediction markets face growing scrutiny over how they prevent wash trading and fake activity.
The incident highlights challenges in policing blockchain-based betting platforms.
