Policy: Enforce Genetic Purity
By - etra_kurdaj
Generally when you finish a genetic mpfiication project all members of that species, and those that are growing will change to that template. That species should remain genetically pure, if you're seeing variants popping up it could be due to a pop finishing growth at the same time as the genetics project finishes and remains the old type, but I think they fixed that, the more likely cause for these deviations is if you have migration treaties with other empires. Those empires contain the old variant of your species and can migrate back to your empire causing that growth of a deviant subpopulation.
Another common way to get those old pops is any in-process colonization. Colony ships in the construction queue or en-route to their planet will have the old pop template on them still.