In the case of embryo cloning, it's Sophie's Choice but for embryos. Make a few dozen combinations of sperm and egg, and then choose the best one to grow based on your opinion. But embryos are people too. How many potential sibs can you waste for the perfect child? It's icky, and we should have caution when we do powerful things.
Individual gene editing therapies are also being worked on now, but these pose similar issues.
What if taking away depression from the next few generations causes the human population to no longer produce quality artists? Another issue: the wealthy will have unequal access to it compared to others. We can only have nice things (freedom from disease) if there are those willing to ~~pay~~ charge for them. Not everyone can benefit from gene therapy, so it is not truly a benefit to society or humanity, and therefore should not be developed as a biotechnology. As if that ever stopped anyone.
I don't know anything about those race mods but i had a similar problem. I don't think the Yttakin gene is related to the issue. They're a type of human, like the other biotech races. I would check the storage filters on the freezer- if it disallows rotten human corpses, the stockpile won't count the rotten corpse even if it allows fresh ones.
The second thing I would check would be the bill details for cremating corpses. The rotting stranger might not meet the filter for the bill's ingredients.
Hope this helps! Good luck!