In my opinion, it is actually the fault of the general contractor or their site manager; there is a reason why the association for surface heating has issued an information sheet called Schnittstellen Koordination Flächen/Fußbodenheizung [interface coordination surface/floor heating].
In the area of underfloor heating, three trades come together: screed layers, heating engineers, and floor finishers, whether that be the painter or tiler.
And here, a site manager or general contractor should actually ensure that the trades work hand in hand for their overall construction.
In the worst case, everyone has tunnel vision and thinks or relies on the other. And that is despite the fact that each of them has more or less the requirements in their own trade-related standards, guidelines, or installation instructions.