The big advantage of Mobius is having random variables in the question, so that students get given different questions. However, when it comes to picking those random variables, Mobius has a habit of choosing pretty much the same ones for quite a while. On a choice of two, it would not surprise me to get the same one 7 times in a row. This results in students being asked the same question after all. The distribution of questions among the available possibilities should be more even.