I have a legacy console converted world, and as of bedrock 1.8.0(possibly earlier) even after loading in new 1.8.0 chunks, all overworld hostile mobs have been spawning in the nether. This includes Zombies, Spiders, sometimes a Witch, Creepers, and Slimes, alongside regular nether mobs.(Skeletons are supposed to spawn in the nether)I play using an xbox.
Happening to me as well
UPDATE: For me, at some point since 1.8.0 came out, drowned started dropping nautilus shells again.