Q: 2014 Prius 2 transition electric to gas is not smooth while driving

I would initially suspect an engine fault (or even something as mundane as bad gasoline; did the incident perhaps start after re-fueling?). There are some technical service bulletins relative to your model describing rough engine operation that was due to EGR system malfunctions but also related to the design of the intake manifold. In instances of customer complaint, a redesigned intake manifold was installed. There have also been software updates. What you are describing may relate to simply rough engine operation but such could be intake, fuel, and/or ignition related. What I would suggest is have this diagnosed as rough operation and the responding certified mechanic will perform the required diagnostic steps to get this resolved. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.