No head for alien sim

That's a new one! The answer is typically going to be some kind of default teeth or lashes or eyes mod that's not properly updated for Aliens. Try deleting your default body part CC, clear localthumbcache, and reload. You might need to also apply new EA defaults. Some known broken ones without available updates are in Previously Broken mods and CC , and anything before the date listed there for issues with Aliens is suspect.