Hostile mobs not despawning (possibly)

I loaded my world into MCPE viz and when I turned hostile mobs on I notice the entire world was full of them, not just within 128 blocks around me.

I also very rarely encounter mobs while caving and my mob farm hardly ever has anything in it.

It's possible that that this just has something to do with how the game is saved and how MCPEviz reads the data, but might be worth looking into.