Enemy mobs spawn in the Deep Dark

I was playing in my world yesterday  (Xbox version) when the update came out, I went to explore to find an Ancient City and I did, when I entered everything looked fine, but as I got deeper through the structure I founded a lot of enemy mobs that spawned right inside the biome, that should not be happening, in the java version that fatal error was repaired a few snapshots ago. 

I even tried it on my computer and it's the same result

They are NOT spawning in any other place and walking to the cities, they are spawning right inside of the biome / structures 

Thanks for the attention