Organize construction electricity/construction water yourself?

Why zero degrees? You will have that anyway later... it should not permanently fall into the higher negative ranges. But it doesn't do that either, instead it is normally regenerated again and again by the control, where then the heating element takes over alone.

Had around -3 degrees at the maximum - currently 13-14 degrees, so fully regenerated again.

The argument that there is a significantly higher heating load during screed drying than during standard operation seems plausible to me. That the probes and the surrounding soil freeze over several weeks under this enormous load would not surprise me. That something could be damaged by this frost damage is probably not to be excluded.

The load is not that high. If it is 10°C outside, the load is not higher than normal heating at about -5°. So that's not an issue. My probe is 95% in "soil", which consists of rock. Nothing freezes there.