Damp walls in the basement of a new building - construction execution error?

Hello everyone,
I'll start chronologically:
Background: 3 weeks before day 0, the screed was "laid". Also in the basement.
The basement is a "white tub", meaning the base slab is waterproof.
Day 0: I notice that moisture rises the plaster in some corners of the basement.
The plasterers had still fetched water in the basement at that time. The suspicion was therefore a leaking hose or something similar.
Day 1: The underfloor heating is filled with water, meaning the water cannot come from the underfloor heating, as it was previously unfilled. The pressure was also constant.
Day 2: The level at the walls has risen slightly.
Day 5: The underfloor heating is put into operation, also the basement area with moisture. The hope now was that the moisture would decrease due to the warmth.
Day 8: Moisture still present...

It has also not rained since day 0...
What do you think? What could it be?
Construction defect? Or does the water really take that long to dry?

Yes, you can say that out loud. But I haven't actually given up hope yet that it will still dry out. Some spots have improved, while in others I couldn't notice much change. I will have certainty at the latest with the next rain. What could be the worst-case scenario? By the way, the house will be built turnkey by the developer.

Do you have pictures of the construction of the basement?

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

Please opinions on this. How can it be that the slab is leaking? How can something like that be repaired??

What does the site manager say?

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

Otherwise: Expert - You can still take action ...