Did my life and all until I had to kill some fishes. I discovered every parts and it started to say "no need to explore anymore" but I still had one nest left.
Well, when you're going to try every bit of map to know where the missing nest is the screen become and stay black.
You can actually still move, exit, speak with a npc (a guard I guess) but the screen stay black.
When you actually find the missing nest everything is good. The black screen is only for already completed nests.
When it happen the only solution is to not move too much and try to figure where the exit is. Then, when you've the text for exiting just do it and try another map.
(even if I truly love to go back to a place and see how our actions changed it, in this particular case I think it would be better to "block the access" to the zones already completed. Maybe reopening them again after the quest)