My eyes are playing up today but from what I can see that looks like steam from the screen blower (and if it doesn’t smell that makes me think it’s steam). Could it be something as simple as water in the air duct somehow, from jet washing too near the scuttle? A wet cabin filter maybe. Only other thought along those lines would be heater matrix… has yours got the dreaded silca sachet in the expansion vessel and is it still all there? Although would that cause a leak and this misting - not sure, generally just blocks it I thought.