Clarifying the in-between rafters insulation
With two much insulation the vents can not do there job making sure there is an air flow path from the soffets to the ridge / ventilators needs to be the first repair / change. Even with good ventilation with cold temps you have may have issues that require Ice &amp; snow melting heat tape. I used heat tape on my home and under some gutters to prevent ice dams. It sounds like. You need to clear some insulation to allow the vents to work.  Then if the ice dams continue heat tape will be needed.  Both poor ventilation and ice dams can create damp and or wet areas you describe, I would add the heat tape in the ice dam area this summer but that can cost a bit to have a circuit installed and the tape put up. Moving insulation can be a nasty job but dosent cost and may do the job If rafters are wet at locations other than the ice dam.