a 5 pound package of hamburger. I suspect, given it is walmart, it was one of these:
that's a pretty big item to not realize has not been processed.
as to 2 sticks of butter: didn't know they sold "sticks" of butter. half pound box, yes, separate sticks, no. That alone would throw up a red flag.
there was simply too much to argue; I didn't see it.
additionally, when using a self scanner, you have to put the checked items on a scale. If you remove them before paying you have to have an attendant come over and unlock the scanner so you can continue checking out. If OP did this and was putting bags into their cart, that is an red flag for the attendant to watch that person since so manner people use the "oh, I didn't see it under [whatever]" in an attempt to avoid prosecution
but a 5 pound roll of burger? Sorry but there wasn't any place for that to hide.
additionally it is a given there are cameras watching each scanner. The video is likely to be very telling.
but as to using the self checkout with a lot of items; it seems our local walmart closes the registers except for the self check after about 10 pm. If you have 12 carts of groceries, you get to use the self check. PITA.