Here’s the solution that works:
Before playing the animation. removing the neck animations within the _targetedAnimations array (inside the AnimationGroup) allows the rotation to persist. See the following code snippet:
animation._targetedAnimations = animation._targetedAnimations.filter(tAnim => tAnim.target.name != "Neck");
Thanks to some insights shared by Kyle Wetton at the following link: How to Create an Interactive 3D Character with Three.js | Codrops