New cement screed wobbles on new underfloor heating and insulation

There is no "screed program" as such, but there is the "interface coordination for surface heating and surface cooling in buildings," where practically every conceivable step for the creation of a heating/cooling screed is described. After that, the screed is initially subjected to slow functional heating, and after its completion and 2-3 rest days (without temperature supply), the readiness-for-cover heating is carried out. Afterwards, a screed should have reached sufficient maturity – but it does not necessarily have to. Therefore, CM residual moisture determinations must be carried out; for heated screeds (I exclude cooling screeds here because this form of tempering has not established itself in practice), appropriate (harmless) sampling points during screed installation must be marked with plastic flags. And if the floor still creaks after the parquet installation, the parquet installer will have to deal with consequential damage. Because they have the inspection and duty of care regarding the substrate. What could be "running" here is a deliberate shifting of risk onto a subsequent trade. If that were the case: a shabby procedure (by the previous contractor and towards the client as well as the subsequent trade).
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Regards: KlaRa

Thank you for your answers! Unfortunately, they do not answer my questions. Can cutting or watering have a chance of success?

Tiles in plank format are being laid, not parquet. With parquet, I would be less worried, but for tiles with a length of 120 cm, it simply has to be solid. As it is now, the tiler will not lay anything in that spot and I wouldn’t want that either, because the tiles would definitely break.

The screed heating program was carried out exactly as the screed installer ordered. It ended today and now there are at least 7 days until the tiler arrives. So that should definitely be okay.

So pouring water on it - oh miracle - did not work.

I don't know if anyone here is still interested. But I'll write anyway how it ended. A cut was made in the screed, then the wobbly piece was broken out and new screed was poured there. Now it is firm.