FYI: I fixed this by dragging a fresh copy of the asset into the scene (i.e. no transformations/scales etc on it), duplicated it, added lattice then coppied it over all other relevant instances and no black stuff!
FYI: I fixed this by dragging a fresh copy of the asset into the scene (i.e. no transformations/scales etc on it), duplicated it, added lattice then coppied it over all other relevant instances and no black stuff!