Hi cretin.
The problem is twofold.
First is that the method Pfizer used to amplify the mRNA for the approval from the FDA used a fundamentally different method from the one they used in production, because the pilot method wouldn’t scale to the quantities of product they needed for mass production.
Second is the detection method used by Pfizer had a limit on how small of a fragment they could detect, about 100 base pairs long. One of the most worrisome fragments, a subsection of the SV40 promoter gene, was 72 base pairs long.
And you will see some persons argue that the concentration of contaminant DNA fragments is within tolerances. But they omit that for the mRNA vaxes the contaminant DNA is carried in the nano-lipid particles so it gets inside cells rather than being cleaned up in the blood like other blood-borne contaminants that cannot penetrate cell walls.