I think this one has been happening for a while. The new smoothness of the game makes it even more noticeable though.
I was flying around the road of materials blasting things with the max powered weapon laser until my fps hit single digits. My astronaut slowed to a crawl. Suddenly, I get a huge burst of speed and I'm able to change direction and accelerate to an insane degree. Within a few seconds though, speed returns to normal.