Short description:
Roads build after christmas event started tend to disappear partially after a while (might be after you reload your map). Intersections seem to be the first thing to go, but I've seen other parts disappear too. (This is not the same as roads disappearing beneath mud and grass)
Screenshot:
Possible cause:
Unknown
Prevention:
Unknown
Workaround:
Thanks Vodkat, that worked for me as well
Related:Original thread(s): 1