I have noticed that the Fog of war seems to reset on the map if you log out of steam and someone else logged into the game for them selves with their own steam account and copy of the game.
Every time I let me kid play atlas on the computer and is logged into their steam account all the progress I have made clearing away the fog of war is reset. It is very frustrating to say the least. I have been able to recreate the issue every time. I have tried re logging, death, and saving my local profile and loading it back in. Non of this worked. I still have all the discovered island names but just cant see them.