By fundamental design, tokens cannot be "lost" as a result of a swap.
Before swapping, users can see how many tokens they will receive. In addition, they have the ability to control "slippage tolerance" settings, adjust swap amounts to minimize price impact, and also control gas fees (aka transaction speed). If prices change while your transaction is pending and the result returns less than the minimum amount required, the entire transaction will revert. This can be prevented by using the ‘partial fill’ function, enabling fractional swap of your assets.
Please note: The gas fee on a reverted or failed transaction cannot be returned.