Natural Site Shiny Rock Excavation BUG

[Aliza]

I'm new to the Excavation Sites just reached 1,000 discoveries, when I started the shiny rocks of each of the Excavation Sites would spawn random tier pokemon or shiny rock exclusive pokemon without a problem. Except for Natural Site I've had a shroomish run away from me because I was too inexperienced, from my experience with the other shiny rocks I'm under the impression that shiny rock has no restrictions for encounters. If this is a bug I would love for it to be resolved and fixed thanks so much.