I don't think this exists. If it did, I would think that you would hear about it more. I'm having horrible luck myself, 3700 for Rookidee across two consoles, one hacked and one not, so I think you just have bad luck.
Edit: I think the odds aren’t 1/683, I think the shiny chances are coded incorrectly because of this tweet:
but I don’t have the game’s code, nor would I be able to understand it. I would just switch to Masuda method