Mobs not Spawning

Hey guys, how are you doing? 

So, this past week, I had a problem with some Mobs not spawning. First I notice that near the cave entrances there were no Bats at all, and that they would never spawn. Then, sometime after that i tryed spawning some Treeguards with woodie (chooping down +100 trees) in autumn, but that didn't work. I tryed again and again, and it still doesn't work. I am not the luckiest person in the world but I think that is a little bit too much. Has anyone had the same problem? Thank you for reading this (it's my first time reporting in here).