just posting this for informational purposes in case other ppl have similar problems:
one of the last blizzard patch broke the appearance of numerous units in my mod, that were using "select texture by id" in their actor to switch textures to dark protoss textures ("dark specular", "dark emissive", etc.)
after searching around what might have caused this, i ran across a data field called "Texture Declarations" in the models that was empty for all the models i copied
this field used to be empty - i already copied values from the original model in this screenshot
this caused the models being unable to attach the alternative textures. units where i used the original model did not have this problem.
my best guess is, that this field did not use to exist, and thus was not copied when i copied the original models?
my second best guess is that blizzard changed something in the way values are inherited from parent values? (which could potentially be disastrous for mods?)