Despawning/Spawning bug

Whilst exploring far out in the overworld (Not too far, like a couple thousand blocks) and in my nether fortress, mobs have not been spawning and even after restarting my game and moving far away, they do not despawn either. This is in a normal survival world with no 'cheats' even being available. I have not found any helpful information on this topic online. Thanks for helping in advance.