@elch Just heard back from the development team, I'm pasting their response below. I'll also attach their files.
There is a set of adjacent Roadway (Straight) and Roadway (Curved) objects as an attempt to model a complex roadway consisting of straight and curved sections.
Actually, the Roadway (Straight) and (Curved) objects are not suitable for modeling such complex poly roadways as it is hard to vertically align the separate objects/road segments (as every separate roadway object could be sloped differently). As a result, the site model recognizes modifiers conflicts exactly where the separate roadway objects align to each other. In such cases, it is preferable to use the Roadway (Poly) object which models continuous roadway along a polyline and overcomes the vertical alignment issues.
The Site model collects modifiers from a custom set of layers (see "modifs_from_custom_set_of_layers.png”) which includes the "modifiers” design layer.
This means that all modifiers from the "modifiers” layer will be recognized and collected by the site model no matter this layer is set invisible.
Notice that there are modifiers from the "modifiers” layer which overlap some of the Roadway objects, i.e. they conflict with some of the modifiers that comes from the roadways.
Please see the attached "Research_Conflicts_Reasons_1.png" which illustrates why the site model recognizes conflicts between the modifiers it collects.
I have prepared a fixed version of the file (see the attached "p80III_modell_fixed_v2019.vwx") where:
The set of Roadway (Straight) and (Curved) objects are replaced by two Roadway (Poly) objects (they follow the same path and model the same geometry).
Some of the 3D modifier polygons in the "modifiers" layer are slightly reshaped (using the Reshape tool) so they don't overlap any of the roadways.