Spawn mobs in Players structure

Hello I have a problem with the appearance of monsters in my constructions (mobs tower/creeper farms) there is no monster that appears in them, I also noticed the objects thrown then when we away remains present indefinitely (even after 240 days of play)
I guess there is a problem with natural appearance in player builds
Thank you, I hope you can solve my problem because it’s really not pleasant to be able to use this great game