My understanding is that it is tied to frame rate stuff. So if you had any hitches during reveal it can like... bug out that part of the save. We will look into it as it's not 100% consistent like I would like.
Started a new game and it reveals the fog now.
No clue if it was the hotfix, random space magic or eldritch coincidence.
I shall now go to the island to pet more fluffies.
On a side note is Mallo supposed to remain invisible during fun time?
For now yes. We will consider adding a button for her once we get the sex options menu in place.