ᐅ Damp Walls in a New Basement Build – Construction Execution Error?

Hello everyone,
I’ll start chronologically:
Background: 3 weeks before day 0, the screed was “laid,” including in the basement.
The basement is a “white tank,” meaning the base slab is waterproof.
Day 0: I notice moisture rising on the plaster in some corners of the basement.
At that time, the plasterers were still fetching water in the basement. The suspicion was therefore a leaking hose or something similar.
Day 1: The underfloor heating is filled with water, so the water cannot be coming from the underfloor heating since it was empty beforehand. The pressure was also constant.
Day 2: The level of moisture on the walls has risen slightly.
Day 5: The underfloor heating is put into operation, including in the basement area with moisture. The hope was that the moisture would decrease due to the warmth.
Day 8: Moisture is still present...

It hasn’t rained since day 0 either...
What do you think? What could this be?
A construction fault? Or does it really take that long for the water to dry?

Yes, you can definitely say that.
However, I haven't given up hope yet that it will still dry out. Some areas have improved, while others haven't shown much change.

I will know for sure after the next rain.

What could be the worst-case scenario?

By the way, the house is being built as a turnkey project by the developer.

Do you have any pictures of the basement construction?

In the last picture, you can clearly see the spot. It was already damp there. Oh, I didn’t notice it back then...

Please share your opinions on this.
How is it possible for the foundation slab to be leaking? How can something like this be repaired?

What does the site manager say?

Or: Could it be that the walls are still drying?

Otherwise: Expert - You can still negotiate...