Thank you in advance for any help you can offer me.
I created an Unlisted YouTube Video to explain the problem and with visuals since its hard to explain.: Character Animator Head Scaling - YouTube
The odd scaling is mostly or all in the Y-Axis, it's hard to say for certain.
I have tried changing all of the strengths from 100% to 0%, testing, and then back to normal ranges. But to no avail thus far. Perhaps I missed one, or a different setting. My only added triggers are for keyframe cycles and head turning.
So if you set _all_ the Face behavior's Strength parameters down to 0% (at the same time), it's still happening? What version are you using? It's displayed in the menu bar. (Beta 6 is the current version)
If you're willing to share your puppet (File > Export > Puppet...) here or via direct message, we'll take a look.
I hadn't tried all of them on face. Setting the mouth strength to 0% solved the problem. Thanks!