Paint thickness isn't relevant for this problem, but maybe nice to have. Get a written report from a well respected paint shop.
Toyota had a huge problem with this a few years ago and I did a few Citroens that had the same issue. Something goes wrong in the factory, either product or procedure, and the paint just doesn't stick. Generally happens in batches so kind of surprised yours is the first we've heard of.
If work is so terrific, why do they have to pay us to do it?