My vamp male sim got abducted and had an alien kid. The kid aged up and has its alien powers like normal, but when I went to CAS and tried to alter its disguise, the kid started to have the vampire growling animations and I couldn't alter the disguise. I checked its traits, and it had both the alien and vampire trait. Has this ever happened to anyone? I might age it up to a teen to see what happens. I do have some mods (mccc and a few no autonomy), but its all up to date and never given me issues before.
Edit: I aged him to a teen and he seems to have both alien and vampire powers.

I read someone at the OF had this too, apparently it's a glitch, because hybrids are not meant to exist - the glitch with both alien and vampire powers only appears when the vampire is abducted by aliens. Your sim is a freak of nature. Congrats! LOL
Be careful about loading the sim in CAS until they've grown up though, it can mess things up.

Yeah, I tried loading him to edit the disguise, but it wouldn't even let me edit the second form. I guess it was conflicting with its vampire dark form. It's cool how both the alien and vampire powers work though.