It's just sad that when it comes to casino withdrawal issues like that, especially the big amount in question is the length of the process that the casino platforms do before they approve you to withdraw, and there's nothing we can do about that because they hold our account and balance assets on their platform.
Casino has the right to review the withdrawal of any account if they want it. His money will still be intact on his balance if he didn’t wager it all and lose. The point here is he just to put the blame to the casino by locking his funds while he can recover it if he just wait for the process. Stake has a lot of high roller player and I’m sure they will post a complaint here once they experience same scenario like OP which is not the case here.
Stake withdrawal is instant even on higher amount than OP money. The OP account game history probably has some unusual activity for Stake security alerted.
The OP is already offline for almost 3 weeks. I guess he already accepted the loss.