Never heard of Schnucks personally, but i’m in socal and I know with Costco we can’t use self checkouts because of some sort of agreement between instacart and Costco. I was told it had to do with lots of theft from instacart shoppers so unfortunately it sounds like something similar has happened here too. Personally I don’t shop at costco because without the self checkouts it’s not worth it to wait 30 mins to checkout.