They announced they reopen:
https://www.okex.com/support/hc/en-us/articles/360052758931-OKEx-Official-Announcement-Reopen-of-withdrawals-and-other-related-updatesIt's still quite vague, but it seems to confirm that the issue was the arrest of Star Xu. Their description of the key backup is quite worrisome, still:
The reason for the suspension of withdrawals in this specific incident was because a private key holder was not able to authorize transactions. OKEx has always used a backup mechanism for private key holders to ensure that each private key holder can trigger the activation of the backup private key in the event of long-term incapacitation, such as death or memory loss.
However, we unfortunately failed to include other specific scenarios, such as private key holders becoming unreachable due to unforeseen circumstances in our contingency plan. In this specific incident, therefore, the ultimate resolution for the private key holder’s short-term incapacitation was not a technical one.
What does that mean? I interpret that they have Star Xu as a necessary part in both the main and the backup paths. That if his main co-signers went missing, he could "trigger the activation of the backup" but only he was able to do it.
That could be read, alternatively, as that there were timelocks involved. However, I think that's not the most likely, for many reasons: they don't explicitly mention timelocks, their known cold wallets are plain multisig with no fancy scripts, suspension covers all coins not just Bitcoin, etc.