Damp interior wall after completion of exterior plaster

Hello dear experts,

I am a bit puzzled. About 2 weeks ago, the exterior plaster on our new building was completed (mineral plaster).

Now I have noticed that the wallpaper on a wall in the living room has come loose. I peeled off the strip, underneath it is damp in places. My measuring device gives values up to 120 digits. There are no water pipes or anything similar running in this wall. I have now created a measurement grid; towards the window it is dry, the moisture seems to be rising from the bottom straight up the wall. But above a height of 1.50 m everything is dry again. The wall is between two windows and about 1.5 m wide. The building block is Pumix with perlite filling.

It hasn’t rained for days either. Where could this moisture be coming from? Possibly residual moisture from the plaster?

Best regards
Basti the desperate builder

Underfloor heating leaking?

Joints of the floor and base tiles are dry, system pressure is constant, I think that can be ruled out.

Strange is that the moisture in Höhr 1m is the highest (120), in the base area we are at 70.

Perhaps you should provide a few more details. Which lines are nearby ([Grundriss])? How long did the interior plaster have to dry?