Your slippage tolerance is not a safety setting. It is a public offer stating the worst price you will accept — and something is always willing to take it.
You swap $10,000 on a decentralised exchange with slippage tolerance left at the default 2%. The quote looked fine. The fill comes back noticeably worse, and the price snaps straight back a block later. Nothing broke. You were sandwiched, and you consented to it in the settings screen.
— Educational, not financial advice.