When animating the look at constraint work sometimes and sometime don't.
My process:
1. Start animation with custom character CC3+ (Created in CC4.52)
2. Apply a talk animation from the libraries (Standing Talk)
3. Try to apply Look at camera or target

It don't work.
But work perfectly with characters i created with the same methodes one year ago.
I used the same blender pipeline to create thos characters.