I moved my world from 18w16a to 18w20a and the same thing happened to me. Hostile mobs don't spawn. So I went to chunks that have not been generated before and hostile mobs spawn there fine.
It appears that hostile mobs don't spawn in old world generation. But they do in new world generation.
I moved my world from 18w16a to 18w20a and the same thing happened to me. Hostile mobs don't spawn. So I went to chunks that have not been generated before and hostile mobs spawn there fine.
It appears that hostile mobs don't spawn in old world generation. But they do in new world generation.