you are ventilating open air/oxidation and chip chinese pcb and here is result.Winter times even you think dry there is many particle in air can make oxidation fast, chinese pcb are not protected from oxidation.and also it looks like water leak happened.and also measure humidity outside too.Rigs dry air fast so measuring it inside will be not accurate.
Checked the roof and definitely no leaks. Must be the cold air I’m drawing in. I have ordered a 25L dehumidifier which is coming tomorrow and will place it directly in front of the cold air feed and see if hopefully this helps. Ideally I would box up the air intake, tunnel it through dehumidifiers then pass it through the rigs but i haven’t got time to make this right now.