[bstark]

Unless I'm way off base (happens often) that is your bathroom/biffy power vent exit, the one you turn on so as to avoid embarrassment after a dinner of baked beans produces the predictable results!

Proceding along that thought: there should not be any blockage but quite often the underlying roof insulation was not cut away to provide a direct flow of exiting air from the ceiling mounted fan. I removed my fan assembly from the ceiling in the biffy and stuck a flashlight down the pipe in the roof to accurately locate the route the air needed to take to make a quick exit and in my case it was about 10" away from the fan port so I cut a large plastic jug in half and removed the bottom and top portions to fabricate a type of duct/dome to hold the insulation away and allow the air to get right to that pipe's bottom end to minimize how much moisturized air went into that attic insulation.

The hard crystallized stuff you mention does not ring a bell as the attic insulation is your typical beige colour of fibergalss batting.