You assume you are trying to run the bank profitable. But maybe you are just a very good friend, of another bank, that wants to see your bank bankrupt?
You just discovered the concept of natural monopoly
If I go to any bank to withdraw $50000 in cash, they won't let me either.
You just need to give advance warning, and perhaps pick up the cash at a big branch where the bank has good security.
This isn't difficult.
Getting this gold is not difficult either, on the state scale of difficulty. It's just not that easy like your uber eats delivery.
Surely gold is different from just account balance right ? They promised to actually keep those gold in the vault, and not spend the gold and keep only the equivalent in bank notes.