There’s a ghost art unit at the USPTO. It has patent applications assigned to it, but it has no Examiners. If you have the bad luck to have one of your patent applications assigned to this ghost art unit, the application will never get examined. At least, it will never get examined for so long as it sits in this art unit.
At our firm we try to track the FOAPs — first office action predictions — for our pending patent applications. We try to keep track of which art units are bogged down and which ones take up new applications sooner. We stumbled upon the existence of this ghost art unit when we kept noticing that some of our pending applications had no FOAP at all.