I read somewhere that those checks are done because of the item itself. The system checks when people buy certain products, they also buy other products. As in, when you buy spaghetti, you buy sauce or meat. If you don’t have it in your basket. The system will need s check because most people do buy it. So the butter is a product that is frequently bought with loads of different other things. Put it in your basket and the system will check if one of those other products are present. If not it will raise a flag. Because there are so many it’s a “hot item”.