I would guess your GPA had a big part to deal with the Pro N, they can be very picky, my guess is the first time you did well on the interviews but your GPA led them to pass on you, but good enough for them to take another look, but then the next round was probably still very competitive which led to the second "N"
I had several candidates that had GPA's in the mid to low 3's and every time the accessions officers said they were concerned about the low GPA, but would see how they did on the interviews.