Unity 2018.2f8 I'm using the cinemachine free look camera for third person shooter game. Now because free look camera doesn't have a offset rotation I had to add a Head object to the player with a child object called look. I have the cinemachine camera following and looking at the look object. I then have head object rotate around the Y Axis to get horizontal rotation in the PlayerController script. I have the cinemachine camera control the vertical rotation. This is where I have the problem when rotating horizontally the vertical rotation starts jittering. If some one could help me that would be great. I provided the project in a unity package below with the sample scene.
I think it's just because your max speed on the FreeLook Y axis is too high. Small vertical jitters of the mouse get amplified. Just turn down the max speed, or give it just a tiny bit of accel/decel time.