When I add in tutorials I will explain it a bit more but it's intended that levels past 20 don't increase stats for Chica. Carla also doesn't gain stats but she has more chip slots. I'm pretty sure when you hit level 20 a dialogue box is supposed to appear briefly explaining that you won't gain any more stats for Chica. I know it's there in the latest version.for some reason after reaching lv 21 or 22 i dont remember well but the stads of the protagonist dont increased anymore (at the time of posting this comment I'm lv 26 and still no change. if i am missing something pls tell me) and carla-cake ally at the start of the game when she levels up she doesn't get any change in stats but Chica does.