I would say "a blessing in disguise." The water ingress, being under the vapor barrier, ended up in the intermediate screed. Although it is an anhydrite screed and therefore hardly soluble in water, I still suspect, since no water penetrated for a long time, that it is only some dampness and not wetness. A good sign is also that some of it ran through immediately. The time delay from the start of the rain to the penetration was probably caused by the backup in the window profile and the flow only starting at a certain level. After the rain, drying likely occurred again, and during the next rainfall, the backup happened again.
Some may still remember that the lift-and-slide doors (HS) were all delivered at the wrong heights (too low). We accepted and installed the three HS of the children's rooms in the basement despite the wrong height. The error is not found there. The defect started with the four newly delivered HS. Again, a blessing in disguise that we took the windows in the basement despite the defect (completely without any cost reduction, "mercifully"), because there we would not have had water drainage by means of a lamp drill hole. I knew this karma exists .
The next step is to turn to the window manufacturer.
Thank you for your sympathy; we were (are) devastated! But we will probably come off with a black eye.