2017 Ford Fiesta with 5 speed transmission. Vehicle has loss of power and shuts off. Ford dealer has no idea what the problem would be
Then find a smarter Ford dealer. You can take the car to any Ford dealer for warranty service. If they can’t fix it, many states and countries have laws that make them buy the car back.
Also read the owners manual for the procedure to elevate this complaint higher up the corporate ladder if you can’t get satisfactory service from your local dealer(s)