The other walls in the room, same paint, same conditions, do not have this happening. It is very very odd but I’m hoping someone has an explanation I haven’t thought of. Oh & it was there when I moved in. I wiped it off and then it reappeared slowly, dripping down again, over the course of weeks.

Is it an external wall? Could it be small amounts of condensation that build up very slowly?

Is there an ac vent blowing on that wall in another room? Like, 🌬️ | 💦