Are these products officially intended for Poser 11 or earlier versions?

Some creators make hair in ZBrush using Fibermesh. SuperFly doesn’t handle converted Fibermesh-based hair very well, because the strands are extremely thin and the render engine has trouble transmitting light through them.

You can usually test this by going into the Hair Room and changing the density or length. If those settings have no effect, the hair was most likely created in ZBrush. In Poser 12 and newer, this kind of hair can be particularly difficult to render.

Essentially, Poser and the render engine are trying to convert the Fibermesh strands into dynamic hair strands, which often causes issues. I’ve encountered similar warning messages myself in the past.