There is possibility of chemical residual effect.
Sometimes, early packages need be removed from the line;
and at that pointsome packs may show similar type of problem/s.
Or, treatment of paper when pass through hydrogen peroxide bath
may be insufficient, which can lead to high heat resistant bacteria may not be detected
at tepmperatures of incubation while testing? I am not sure.
Handling of packs during transit and internal shifting in shops can lead to micro-damage.
Needless to say, western countires are having best technology and food safety management systems, but,there is a chance of error.
Okey?