my wife's car has a service bulletin on it for the hose on the PCV freezing. The problem is the molded & shaped rubber hose collects condensation in a dip, which freezes, blocking the hose. The fix is to replace the molded hose with a regular bulk type rubber hose, and routed over the top of the engine so it has no dips.
So:
is it rubber? (can you squeeze it to find the frozen part)
are there any dips in what you think is freezing?
can you reroute to avoid dips?