People are usually quick to mention foul play whenever a casino suddenly decides on KYC verification when a gambler tries withdrawing a huge amount, but it is not always a foul tactic from casinos, as it is in line with AML laws, especially in cases where the withdrawal is huge and above a specific amount.

Another reason could be the casino just wanting to ensure that the documents you have submitted before are yours, because if they were yours, you should have them and also have no problems with resubmitting them for reverification.