The most conspicuous one recently was at one upscale grocery chain within the last year. There was what I took to be a dedicated LP person who seemed to be lurking behind the self-checkouts, to watch me specifically, and I stood there until he went away. Then, as I was checking out, this employee came up behind me and very persistently told me that I hadn't scanned something. Annoyed, I pointed on the screen where it showed I had. His eyes went wide, and he spun around, and quickly hurried away, no apology.
If I had to guess, I'd say they didn't code that intervention/confrontation as their mess-up, and I wouldn't be surprised if I still got dinged as suspicious, to cover their butts.
We do seem to have a lot of shoplifting here in recent years. And I have even recently seen a street person in a chain pharmacy here, simply tossing boxes of product off the shelves, into a dingy black trash bag, in the middle of the day. Somehow none of the usual employees around. Yet there's often employees moving to stand behind me at that same store, when I use their self-checkout. (Maybe my N95 mask is triggering some association with masked bandits, yet bearded street person with big trash bag full of product makes them think of lovable Santa? But an N95 is a good idea in a pharmacy on a college campus, where the Covid factories that are college students will go when they have symptoms.)