sims genetics completely different from parents at Ancestor stage

Hi, so ive come across a rather unusual bug where the new borns of sims end up coming out a totally different genetic thats not at all related to their parents. 

I've read through countless hours of posts on here about the black babies or white babies bug that occurs too but its not exactly the same.

To explain my issue , i do have mccc installed. i just have marriage set for teens and the tags chosen in my library of my own created sims to be imported from the tray, but that shouldn't effect new borns and is unrelated to it.

So what happened is i had one sim become a vampire and impregnate a bunch of sims leading to my sim having 30 vampire children. 

Of those 30 vampire children turning into adults, those adults had children as well-which were ether black of a different genetic, white skin with turquois eyes, or plain brown eyes brown hair. Totally unrelated to the parents. Almost as if they were adopted from a mass production toy factory but they weren't adopted as they pregnant and my adoption is off.

Multiple new born babies once aged up looked identical to other children from totally different families.

I thought this was because of the fact they were vampires and of the weird vampire skin bug, but i put that to the test.

This is the strange part, this bug occurred only after a long line of a family tree. it kicked in to all sims vampire , spellcaster, werewolf , mermaid and even human, it occurred to all sims at once even in the unplayed hosueholds. 

No updates occurred from mccc at the time, no updates of the game itself came ether.

I know ill be hit by 'try disabling mccc' i mean i could try that but why would that bug kick in when i never touched mccc at that point and the bug kicked in when the family line became an ancestor stage ?