Sorry, let me explain, Nidoran(M/F) and Volbeat/Illumise gender ratio goes against the RNG reporter completely. Literally, I received a Nidoran(M) from an egg that was supposed to be female(F/F/F/F) and vice versa if it was supposed to be only male.
I even conducted an experiment, but its not done just yet. I'm going to do more tonight. Apparently, Nidoran M/F and Volbeat/Illumise gender ratio if 50%(but not the normal gender ratio, I mean as in something can be completely random, so no matter the egg, it could be 50%). For this one time, I am going to breed Volbeat/Illumises. To test if this is true, I'm going to breed a Volbeat/Illumise on the same shiny egg seed. If I manage to get the other gender, then this may be one of the few things in pokemon that actually is generated randomly. If I get a Volbeat or Illumise no matter what, then it has something to do with the PID(but different from normal gender ratios, like wumple evo prediction, or spinda's spots, or unown's symbol).