I am on the mac version of Pokemon Reborn. The game runs fine on macOS Catalina btw (till now). I am pretty sure this should not just be on the mac and I'm not sure if this is a bug at all but sure seems like one.
I was battling Noel's Clefable, who with elemental seed had boosted defense and ingrain or something. I used sludge wave which turned the grass corrosive and during some of the move spam I happened to poison Clefable. So Clefable was taking damage from the ingrain on the corrosive field but did not take damage from the poison status.