Gamefreak created the most OP Shiny Hunting location... 

I’m starting to think that you are like a slaking or snorlax Because only a obese superfan would be this whinny

Dunno if this is sarcasm or not, but this isn't broken code, this is how the game is intended to play out. Encounter Power Sandwiches are intended to do as they're told, and encounters aren't fixed per entering and exiting the map like in Legends Arceus.