The 2017 ford fiesta is not noted for specifically having transmission problems. however, like all cars, it could develop over time, especially if you do not keep to the maintenance schedule and put fluid in as needed. if you start to notice a burning smell from the engine, the gears grind when shifting, the gears slip when shifting, or it clunks when running then you may have an issue. if you suspect a transmission issue then you need to have it looked at right away. if you catch it early it may not be a major repair, but if you let it go and blow the transmission you are either going to be out a car, or out many thousands of dollars.
The older fiesta models are well known for transmission problems, owners started suing ford in 2017. ford has been working on addressing the increased problems with transmissions requiring replacement early. the 2017 fiesta still has the dual clutch transaxle which has been causing the issues. however, it appears that most of the bugs have been fixed. if you do not want to chance it, buy a manual vehicle, they do not have transmission problems.