Naturally spawned mobs not spawning - built large, dark room, height of 5, with spawning pads, no torches or other obstructions on the pads which are made of solid cobblestone blocks (not slabs) at y-151, ocean biome. Platform below for collection at y-133. There is nothing else around, all other caves within 10 chunks lit up. Normal and Hard difficulty makes no difference. Switched to peaceful and back with no change. Stood at the collection platform for nearly 20 minutes without a single spawn. Tried waiting closer - nothing. Tried waiting a bit further away - nothing. 

This is a continued issue as of last night - Nov 14, 2018. Game is updated to current version (1.8.0.14). Was marked resolved on a 1.8.0.13 post as being addressed in the latest update.  This is not resolved in the update. I purchased and downloaded the game three nights ago - after the .14 update. 

Thanks for your help.