I have zero personal knowledge regarding precisely why this occurred.
But generally, at least in the federal District within which I am familiar, it is not that uncommon for a Magistrate judge to rotate judges from time to time.
It happens. It has happened in cases I've been involved in. A retirement or changing jobs is usually the culprit. Nothing really concerning, but I will be a bit bummed to lose Gorenstein. I liked his rulings so far 😉
That being said, the new judge has an impressive resume