I have noticed recently that when I play (set mode: normal mode) that when night falls or when I enter a cave (times when monsters typically appear) I don't see any monster mobs spawn at all, I would even wonder in a very dark distance for some time but i don't see anything. Today I have also noticed that no fishes and horses are spawning just dolphins and turtles, pigs, sheep, chicken, cows, lamas, squids and villagers. This is unusual because before I would see lots of mods, I then decided to change the mod to hard and then easy to see any effects but there was none. I have never played on peaceful in this world and I have kept it like that so I don't know why it's like this.