Is water seeping through the plaster?

With the paved road, a lot becomes clearer to me. Water can of course seep into the gravel and then run into your property through the substructure. Do you happen to have clay soil?

Take a spirit level and hold it against it. How much lower are the icy spots compared to the rest? If it is pressing from below, it must be a larger hollow.

Clay soil is always a problem here throughout the entire construction area, yes. Do you mean the icy spots on the street or at my driveway? I'm currently a bit confused about what you mean by [Mulde].

Is this a current picture or a current problem? Which district? To be honest, I wouldn’t want to judge anything based on that. Southern Lower Saxony has soil that is far too saturated from the heavy rain. And other areas are also struggling with water that can no longer drain and is simply finding paths that are displeasing. It doesn’t have to be flat land. In times of disasters due to rain, rising groundwater, and high water levels, I would simply be glad that the amount remains manageable.

Strange is just that it is only this one curve. The other 4, which are identical except for existing processes in the curve, do not have the problem.

I don't quite understand the part about the public road. It's surely paved and therefore impermeable, right? (...)

No. Especially on less trafficked side streets, cobblestones are often used.

The ways of water are unfathomable. It could be groundwater that cannot infiltrate quickly enough, therefore accumulating on the impermeable layer and pushing upward. Why this happens specifically at your place can have many causes. Usually, you can't do anything about it, water will find its way.

Consider it a test of endurance. The past weeks were far, far too wet. First the mass of snow at the end of November, then it all melts, December was completely rainy, including heavy rains in many places, and then also the river levels, so the water does not flow away properly either. If this did not cause major problems for you, it probably won't cause problems in the future either. It's just a bit of ice in the driveway, worse things exist.

The paths of water are not unfathomable. They follow gravity and the path of least resistance. This means: for something to seep in and come up somewhere on the side, that spot must be lower than the rest. And no, just because it works well once doesn’t mean it will continue to do so. Paving stones are more flexible than asphalt and can accommodate some movement during frost. Still, it’s not good if water stands in the entire substructure and even pushes out through the paving stones. Sooner or later, you will have frost damage in the form of ruts and loose stones. Not to mention the danger posed by ice sheets to cyclists and pedestrians.