GUI objects jitter when following "lerped" Gameobject [SOLVED]

I have a gameobject being lerped/slerped between two positions and quaternions by an AI script on my server. The Healthbar that follows the monster seems to jitter between random positions sometimes even going off screen and coming back.

How do I fix the jitter-like movement of GUI objects “following” a gameobject?

EDIT: A video showing what happens (a bit hard to see because my game runs at 60 fps and the recorder runsa at 32 fps)

Maybe try setting the position and scale of the health bar only once, on Update() instead of OnGUI()?

OnGUI() can be called multiple times per frame, which might explain the jitter.