Room thermostat moist on the front side

Hey,

does anyone have an idea about this? Recently I saw that the (schon immer) closed room thermostat in the bedroom is wet on the front side, where the control dial is, or rather there is a moist film on it. Below on the wall/wallpaper there is a damp spot. I have never had this before, not with any other thermostat.

Thanks!

What kind of wall construction is this? Can there be drafts through the wall hole?

I don't think so. Interior wall to the hallway on the upper floor, brick. After now 3 years in the house, this is the first time I've noticed it.