Went in to try and get the Return To Sender achievement as it's the last one I need. There was one single, solitary ghast. A couple of wither skeletons, a handful of pigmen, and two blazes. The ghast spazzed so I was unable to bounce back its fireball, and despite an hour of trying no more spawned. I could hear one in the distance but I was unable to find it (got butt-lost trying).

The Nether fortress is deserted. Nothing was spawning inside. Not even from the blaze spawners... The blazes are still inside the cages but nothing spawns. The whole place is eerily silent. The only noise came from a couple of chickens and cows that had come through the portal at some point.