We now have tested all matching Cesium versions (2.4.0, 2.4.1, 2.5.0, 2.6.0) for UE5.1 and 5.2 and came to a conclusion. This might be help for the cesium team:
Cartographic Polygons in Cesium 2.4.0 definitively cuts geometry (or at least the collision), even if it is not intended as you said:) Testet both, in UE5.1 and 5.2
C.P. in Cesium 2.4.1 and all later versions does not cut. Also it does not set the Opacity mask 100% correctly. If the user walks nearby the cutted parts, these partly appear visible with collision. See on screenshots with Ces4.2.1 in UE5.1
The behavior is unrelated to the imported IFC-Building.
For further ongoing, we want to ask if you plan to include such feature as “clipping geometry” in any future CesiumForUnreal version?
Since our project is growing and this feature is a must-have for our customers it would be great to know.