Charles Hoskinson explained that after Attain Corporation’s closure, IOG deemed the legacy redemption process insecure and conducted an off-chain sweep of unclaimed ADA, revalidating eligible buyers through legal and exchange partners as a consumer protection step

Quotes that support claims

The sweep reset the process and ensured all the remaining unredeemed buyers had an opportunity to go through compliance again,” Hoskinson wrote, characterising the measure as a consumer-protection step rather than a seizure.

Because the legacy on-chain redemption mechanism was insecure once Attain closed, the team "swept" the unredeemed vouchers off-chain, re-verifying claimants through local counsel and exchange partners.