Some of my collections of textures in skm format behave perfectly in SU 2016 pro and earlier versions but in SU 2017 pro and SU 2018 pro there is a real problem as described below. (I am on an iMac 5k running High Sierra 10.13.1).
In the problem sets, whatever material I use first cannot be changed for another. If I apply a material to a face and then try to apply another material from the set to a different face in the model, only the first selected material can be used. I can change materials if I pick from one of the problem free sets however.
I presume there is something in the skm file that the later SU versions are reading and choking on.
My workaround is to either use SU 2016 for materials or to use eneroth’s material extractor and drag the resulting model into mine. The extracted materials work OK. The problem with the latter approach is that I need to apply all the materials in the sets to a bunch of faces first in SU 2016 since the extractor only works on materials in the model, not collections of materials.
A better solution would be welcomed.