When you enter 400DAI in Cube 2, your transaction will fail once the swapping result in Cube 1 gives you less than 400DAI, which is not uncommon. Leaving a difference in the 2nd cube input can increase the chance of success significantly. In the "Good combo" example, the transaction would only fail when ETH price drops below $380 (> 5%) between the time you set the combo and send it out.
Using Chained input feature to avoid slippage: