[MCPE-21856] Mob spawn rate low or broken spawn rules

Update on this issue by [Mojang] Mega_Spud (Jay Wells):

Please remember that this is a bug tracker and not a forum for discussion or feedback. Please keep any comments limited to NEW, relevant information only, and add a vote if you would like to show your interest in this issue.

While we understand your frustration at certain game mechanics not working as you would always like or expect, please remember that there is not always a simple fix that will resolve the issue immediately. Please be assured we are actively looking into a solution for mob spawning that will work for all players.

We have put together a post on the feedback site that encompasses some of your most requested features regarding mob spawning - feel free to add a vote there:
Mob Spawning - Feedback Site

If you'd like to discuss the issue further, please visit the Minecraft Discord

Something seems to be still wrong with the mob spawn rates.
It's fine for mob spawners, but for simple mob farms like a 20x20 platform 24 blocks above the player it's still off. I play in hard difficulty and there are barely mobs spawning inside my mob farm/trap. Ii tried multiple positions around it, but nothing really changed except an occasional mob drop every minute or so. The overall spawn rate seems to be quite different from the Java edition.

Mob spawners, like my skeleton farm around a spawner, works great though.

I attached (uploaded) the world, with the player right below the mob farm.
Sadly my world is 12mb big, so I uploaded it somewhere else: http://www.ta-sa.org/files/20170508_mob_farm_spawn_problem.mcworld

Maybe this is a duplicate of ~~MCPE-12422~~, but that one is just open for iOS and not Windows 10.