Further info: Doing a nuzlocke and instead of any wild pokemon appearing in the route 4 hidden grotto i only got 1 item and nothing else has appeared. Plan on using it through my adventure because i have the mega stone.
If you’re trying to save scum for it then you most likely made your save instance after you found the item and left. After picking it up you must wait a day for the contents to reset and save before entering and checking what’s inside. Even then, it’s not too high if a chance so you may be resetting for a good chunk of time.
Im way past it, even returning to it now (im just before the fairy gym) nothing is there. I passed by it like a week ago too. Reason why I figured id ask. In case the rest of this game gets too hard for me.