Here is one I haven't run into yet. In my current game, I am on Season 36. I ended the next couple turns, and suddenly the entire world map was revealed, no fog of war. Unless this is some spell that some AI cast, seems like a fairly big bug. If it is a spell cast by an AI, there should be a pop-up or something to indicate what is happening.
This can be reproduced within my current game.
Save file can be found at: