I have been mineing and noticeing for several days now that almost nothing spawns in new caves. I always go to new chunks couse my world is from 1.12 and I mined everything around spawn. I can tell for sure that something is wrong with spawn rates. In a 2h mine session (not branch minening) I killed one creaper and one sceleton. Nothing at all in new caves. Monsters spawn on surface during the night. Local difficulty in new chunks is around 3. Old chunks around 6.