Facial mesh deforms when head moves// Animation// Rigging//weights


Hi everyone! I need some help, was wondering if any of you know a solution.
I made this model and rigged it, weighted it and it was looking fine all the facial animations looked right. Until I thought I was done and moved the head upwards, the facial mesh deforms.

I weighted everything acording to the animation movement each part required.
Used the UE4 mannequin skeleton and added the facial bones.
Here are 2 short videos so that you see the situation properly.
Anyone know what is causing this and how I can fix it?

Videos are in the link below: