There appears to be some issues with humanoid:ApplyDescription()
when your original avatar has the Three-Headed Trouble head
Here, I’m applying Builderman’s HumanoidDescription to my character which currently has the Three-Headed Trouble head on.
If the sizing on the head isn’t correct when I apply a HumanoidDescription, it’s the neck position that’s off.
Edit: I’ve found that I can reproduce this issue by applying a description that has the Three-Headed Trouble head, and then applying a different one.