Can over fascia vents cause problems?

[chiptech81]

Hi, I live in a 1930's semi detatched house, the roof is pitched on all 3 sides. A few years ago we had new fascia's and sofit boards fitted with over fascia vents. There has been an ongoing problem in the front corner bedroom (box bedroom), at coving/ceiling level more where the wall meet in the corner, black mildew forms on wall and ceiling. This happens in places along this wall, this side wall is the external facing wall.
The black mildew will wash off but will come back. Loft is insulated with 100mm in between joists and 100mm over joists, has good central heating system, window has trickle vent.
The over fascia vents are on all 3 sides of fascia boards im wondering if this is causing to much cold air int the loft, could this be possible?
I am at a loss with this been trying many things for a couple of years.

 

[Alastairreid]

Have you checked the insulation is right up to the corner? it sounds like a cold spot in the ceiling.

 

[chiptech81]

Up in the loft the insulation was layed upto the end of the plasterboard where it meets the internal wall. I was always told to leave a ventilation gap, however i will try and overlap the insulation onto the top of the internal wall and try that. The amount of vents the roof has got and it will naturally vent through the felt it should have enough air flow.
The corner is tight as the rafters join but i stuffed as much as i could in there