The pickup chance is really buggy. I set it to around 30-40% chance with 5 pokemon knowing pickup and sometimes 2 or more pick up items after a battle which is fine. But then after a while, only my linoone was picking up items. So I set it to 100% pickup chance and still out of the 5 pokemon with pickup, only my linoone was picking up anything. So I just left it at that but after a while now, even my Linoone stopped picking up items even at 100% chance.