This is very common. Branch banks maintain a limited reserve of "Cash on Hand" for several reasons;

1. There is a limited amount of printed FIAT
2. Digital transfers have largely replaced paper transfers for high dollar amounts
3. If the bank is robbed, they don't want the thief to make off with more than the insured deposit amount.

If you can't wait 48 hours for a large cash out like that it is somewhat suspicious as most people do not impulsively spend 20k in cash.