Good Morning,

How do I fix hostile mobs not spawning?

I've been attempting to build an effective mob trap for several weeks but always run into the issue that mobs simply won't spawn in it. The trap is located between y=63 and y=125. it is multi-layered, in complete darkness and made entirely of stone bricks. My AFK location is directly over the trap at y=190. The trap is located directly over an ocean so there is no other land for the mobs to spawn on. We have tried turning on and off mob spawning, restarting the game systems and internet. 

What is broken?