Uploaded existing world to Realms. Hostile mobs spawning is vastly reduced, for example, pigman farm high above the nether is not spawning pigmen. F3 shows very low entity count. 

When running the same world locally (form the copy I uploaded to Realms), hostile mobs are spawning.

Render distance is set to 12. 

Difficulty: Hard.

Spawn Monsters: On

This occurs with only 1 player in the realm.