It's hard to be sure, because the level of detail is scant, but one series I know of that meets your stated criteria is the Soul Rider series by Jack Chalker.
The intro from book 5 gives a nice description of the series;
But only the wizards of World, those with the power, could command
anything from those great machines, and they were as limited as
always. None could again get into the great control rooms of the
ancients nor speak directly to the tremendous thinking machines that
ran everything automatically. The Gates themselves were almost an
afterthought; they had been closed, and set to "outgoing," but they
had been locked.
Nobody really knew how they worked, or how to use them, and the
computers had been strictly limited by the ancients so that even if
they possessed that knowledge they could neither release or reveal it.