In regards to both tests #2, please note that both required an Animator Track to sit bellow the Action Track that contains the Look At clip. This is required because Look At is an additive process added on top of existing animation. Without existing animation, there is no pose for the character to return to (blend out to).
In regards to both tests #1, I honestly can not replicate this behaviour if there is an Animator Track bellow the Look At clip (animation needs to exist bellow the look at clip and playing).
Just to clarify are you referring to Animator Track or the Legacy Animation Track? (both should work by the way, but just in case).
In regards to the error, is by any chance the gameobject that has the SkinnedMeshRenderer disabled?
Can you please try opening up CharacterInspector.cs and replace line #74 (the error line) with the following line of code and let me know:
