Its not necessarily the material. TBH I really like EnviroShake. Awesome product and unlike Cedar Shakes mistakes during installation are very visible. The warping is consistent with improper air pressure resulting in over driven fastners or improper fastener placement.
EnviroShakes have a specific location for fastener placement. (Inverted V Mark ) Ignoring that specific location can cause the material to warp. Another possibility is the installer failed to maintain a 3/8" gap between each shake to allow for expansion with the change of the seasons. Fastening a comp shake too close together will also contribute to the material warping.
As far as not purchasing EnviroShakes because the company said they were installed incorrectly by the installer why do people bust on the manufacture ?. If the manufacture has legitimate evidence of improper installation is a bit silly IMHO.
EnviroShakes are very expensive and if the manufacture Rep/Engineer determined the material was not defective and the damage to the material rests solely on the installe. I myself would have to side with the manufacture. EnviroShake is one of the firsr manufactures to produce composite roofing products.
Enclosed is a few pix of one of our EnviroShake projects.