Is it ever stated who the disappearing applicant was?
405 entered the test. 1 was injured. So the 404 was correct. The hunter test is one of survival and cunning etc. the one Hisoka "Disarmed" could not continue with both arms gone.

Essentially he failed the test when he bumped into Hisoka and not apologizing. Perhaps if he had sensed his surroundings a little better, like a real hunter, the 404 would have been a 405.