You sure about that? I used to get them all the time in the middle of the map in 17.0 thru 17.2Yeah thats not normal at all. Must be the mod. In vanilla radiation zones stick to the borders of the world.
I hope that these zones will be shown on the map once you have uncovered them or that you can mark the area yourself. At the moment you can only mark single points on the map but not whole areas.I posted a bug report about it, and they said it's an intended feature, and more will come involving those random rad zones in the future.