The monster deletion screne is a bit glitchy. It sometimes adds in monsters that arent in your collection, leading you to delete others, and represents one with another. Lost a few monsters because of this. Might want to be more careful in the future deleting monsters.
How do you even delete monsters? I have looked everywhere for the option and cannot find it. Caught two of the same one by mistake.
Go to the screen with “Edit Teams”, “Add Training Sessions”, “Evolution & Awaken”, etc. Look in the bottom right and you’ll see “Delete Monsters”.
Be VERY CAREFUL using it. Make sure you have only selected the monsters you want to delete before confirming.