So the other day I had a problem with my map going from completely visible to all cloudy. I think I know why, every time I travel to Solstheim and back to Skyrim the map gets what I call "un-discovered" ... All the places I've been ( which is prob most everywhere ) gets all cloudy and I can't see any terrain/rivers/lakes/cities.. The only way I can fix it is by deleteing Skyrim and re-installing it... every time I go to Soltheim....

Try deleting and reinstalling Dragonborn. I had some problems with it and that solved it.