That’s Detective Viper to you
I had a similar situation. There’s a building in Area Zero encased by tera crystals but Pokémon can spawn inside the crystals making them impossible to reach. I took a screenshot for my friends for proof but a shiny Iron Bundle spawned inside the crystals and I was doomed to stare at it before I reluctantly walked away from it.I had the most rotten luck today; I'm going through the Area Zero mission in the base game and as I was approaching the third research station, a Shiny Venomoth spawned just as I was stepping forward and set off the cutscene, and of course by the tine it had ended all of the spawns had reset and the Shiny was gone. That has really boiled my blood, and I feel as if I should spend some time doing raids and gathering Herba for Shiny hunting sandwiches to make up for it.