If I merge these two vertices together, windshield exports and works just fine: Not quite sure why, is it related to UV map or is it related to geometry data being somehow corrupted and any change fixes it? Only by merging those two it starts to work though, moving is not enough, has to merge them.
No, number of vertices has to change, it just does not want to work with that exact number of vertices, you need to add one or remove one vertice, then it will work, makes sense? Who in their right mind would make Blender work like that, what purpose does this lunacy serve? --- Post updated --- I think that you have inconsistency on upper part of windshield though, maybe this would work better as all the way from down to up edgeflow would be similar, there is like extra vertice/edge up there in a model? --- Post updated --- Or then split whole thing so there is edge at X 0 trough whole thing? Still it is bit odd how mesh works as static object, but not when put to vehicle, can't really understand why that is but kinda can understand that it probably has something to do with way mesh is bound to nodes.
