I haven't heard that phrase in years. There were some growing pains when self-checkout systems were first introduced, but every one I've interacted with in recent memory has been re-calibrated to be much more permissive.

It used to be like that the first couple of years but the newer systems never give me that and feel very accurate.

I used to pickup lunch from Tesco most days. Occasionally you'd find one item that must have been weighed wrongly at the input stage. It would cause an issue every time you checked out. Usually got fixed within a couple of days.

I wonder if they built in correlation of items which on a mis-weighed basket.

Same. Have to have a clerk unlock the machine 3 times on bad days. It feels like the shop doesn't want me to shop there.