When I build a character with a MC in the head (connected to the character’s final composite), I recently discovered that you cannot then nest that character into another group. Doing so breaks the MC it appears. For example, if I had a character riding inside of a vehicle or nested within an element inside the scene, the MC will break. Otherwise, the MC’s are rad.
EDIT: so I was using an older version of the Interpolation Grid Script in one of my builds in this particular job. The new version of the script in 15.0.2 supports nesting within groups. Thanks to the Toon Boom support team!