Built in and fitted wardrobe problems
I have seen a LOT of problems with damp, mould and condensation in and behind fitted wardrobes and built in cupboards on outside walls.
The problem in my opinion is that the wardrobe effectively insulates the wall from the heat in the room making it colder and more prone to collect condensation which then goes damp and mouldy
Remedies; don’t fit on outside walls
leave doors open!,
take off plinths and leave backs on and ensure air can get out at the top,
in extreme circumstances fit small low powered tubular heater inside on a thermostat.