Dancing Hoskuld
Deity
I cannot reproduce this. Can you provide more details and/or an example save?
All I did to test it was start a new game, go into wolrdbuilder (everything revealed), exitted worldbuilder (back to how it was before). I tested with viewports enabled and default size.
No viewports, I had huge map, any map. Enter worldbuilder, exit worldbuilder, everything is now visible. Save and Load and everything is as it should be. the latter is why I can't give you a save.