Way back in time I worked in a supermarket that first trialled self shopping. At the time this was done with special trolleys and boxes and hand scanners people took around the store to scan their own goods. The scheme survived about two years. The system was designed to gradually ramp up rescans by the checkout operators if prior scans had shown missing items. Certain people were clearly making a lot of mistakes (usually with expensive items like Whiskey) but many weren't. The increased waits for rescans for the people who often made such "errors" destroyed the value for everyone else and they became increasingly angry on what should have been near instant checkouts.
Its notable I think that almost all supermarkets today use self scanning despite all those earlier experiments showing that some people would use it to hide theft. This goes very much against the image of the pocket and exit that people have in their head. That was actually very uncommon and being a person who often greeted on the door it was my job to spot them. Most of the theft occurred through items that were smuggled through the checkout in some way.
I don't think self scanning is contributing to an increase in theft losses and the data shows its not. What I think it potentially contributes to is making it hard to identify the theft because there are less employees effectively as the security force. The decline in prosecutions is likely due to these changes that the supermarkets have adopted which they knew 25 years ago resulted in hidden theft.