Forum Discussion
Turbodriver actually did some testing, this DOES happen without mods. Specifically what is happening is that if a Sim has a skin overlay of any kind (rock climbing gear is an easy non-mod method to test and how they did so) it's not applying it properly if the fairy sim's human skin color and fairy skin color do not match. Other occults do not have this issue, only fairies. As for Turbodriver making a mod to fix (as it's a serious issue for those who use Turbodriver's primary mods) it's apparently something a modder cannot fix, or they would. This is 100% on EA.
Until then, the only workaround to guarantee you do not crash is to make sure that your human and fairy form skin tones match. It bites to be unable to change the fairy skin tone, but it's better than crashing.
On the bright side, Turbodriver did do a formal bug report, and it's finally (as of two months ago) been set to under investigation. So there is hope.
Here is Turbodriver's official bug report that fully explains what causes this crash.
https://forums.ea.com/idea/the-sims-4-bug-reports-en/ebn-fairies-with-altered-skin-tone-cause-the-game-to-crash/12463137