I’ve not had ‘furry’ PMC, in any of its forms, but occasionally
there are dark streaks on it, that I believe indicate the beginnings
of a mold. The simplest thing, in that case, is to expose it to air
for a little while (really just a little while, not enough to dry out
the clay) and the mold goes away. You can also wear vinyl or latex
(if you can) gloves to work with the clay. I have never had a
dermatological consequence from using the clay that exhibited those
streaks. I am not, however, a doctor, and so I can only speak for
what has worked for me.
That being said, if I received a package of PMC that was excessively
moldy (or if I were concerned with even the dark streaks), I would
certainly return it to the supplier asap and ask for a replacement
or credit or refund. Some molds are not healthy to mess around with
and it sounds like your PMC3 had a ‘tenant’ that you needed to evict!