Vapor Barrier in Attic

Quick background: house is a cape cod 1 1/2 story brick, built 1939, attic was built in I'm guessing mid-late 40's. The attic floors are oak strip over subfloor, there appears to be rockwool batts (paper side up) in the joists between the attic floor and ceiling below. Knee walls are about 6 ft tall, then, about 2 ft of angle, then a flat ceiling. The areas outboard of the kneewalls are all accessible for storage and have sub floor over the aforementioned rockwool batts. The roof is original painted metal shingles. House is in coastal Georgia. Problem: The roof rafters were all packed some time ago with rockwool batts from gutter to peak, retained by chicken wire and, in some cases covered with cardboard, presumably to keep from getting dusted with the rockwool when moving about in the storage areas. There is no insulation in the knee walls, nor is there any in the ceiling joists. I'd like to insulate it properly but since its all finished with no access to anything above the knee walls, I wonder if its worth removing all that rock wool? It seems to have not suffered any ill effects moisture-wise over the past 50? years, other than rodent burrowing here & there. Can I leave the rafter insulation in place and perhaps have the ceiling insulation blown in? I've already started putting fiberglass batts on the outside of the kneewalls. There appears to be plenty of ventilation in the storage spaces but I can't vouch for the areas above the ceilings. Thanks.

I have two questions but first some background. I live in a custom built, 3 & 1/2 year old, two storey home. The attic is insulated with blown cellulose (R40 for the most part; more on that later), with a vapor barrier below that. I have vented aluminum soffits and 4 or 5 roof vents. My laundry exhaust runs through my attic, and vents out the bottom of the gable end of the roof. The vent is insulation wrapped under the blown cellulose. The only other vent through the attic is the plumbing. The furnace and HRV vents exit just above ground level. This fall I added a humidifier to my mix of furnace and HRV system. The humidifier has an external sensor to automatically adjust to the exterior/interior temperatures. Within the last 7 to 10 days, I started hearing a drip coming from my attic hatch, located in a bedroom closet. I popped it open and noticed frost across a good portion of the roof, mixed with some condensation and, of course, water dripping. The most significant water dripping was occurring right over the hatch but it was not the only place. It should be noted that most of January, we saw temps in the -15 Celcius all the way down to -40 Celcius. The sun made an appearance the day the drips began and temps start to climb towards the freezing mark. I’ve been through two winters in the house without these issues. First question: Can this problem be linked to the new humidifier; is there some link between the increased humidity in the house and the attic problems? I called over the roofing contractor for a look see. He told me that there should not be any frost or condensation and he felt there wasn’t enough attic insulation. So I call the insulation contractor; he tells me I’m losing significant heat through my attic hatch because it is not as snug as it could be. There seems to be about an inch of dead space in both the length and width but otherwise the hatch has insulation foam on top. And if that is the case, why haven’t I had these frost/condensation issues the previous three winters? I did a walkabout in the attic and measured at various spots. The depth is anywhere from 12” down to 7” in spots. I would average it out to 9”. The insulation contractor tells me the R40 blown cellulose depth settle should be about 10 & 1/4”. It seems to me that I’m going to ask him to level it out but, again, why didn’t I have these problems the last three years? Second question: During my attic rounds, I noticed damp spots in the insulation (and a couple of spots had traces of snow) below the roof vents. Is it normal for condensation or snow to come from the roof vents or is this a symptom of another problem? I’m resizing and re-insulating my attic hatch. I’m likely going to get the attic insulation leveled out. Does anyone have any thoughts or ideas on this matter? Any help would be greatly appreciated.