Our new Space Biome update has been released! Please leave us a nice review in the App Store if you have the time, thank you!
Sooooooo that stupid, rotten, no good disappearing mob issue seems truly fixed at this point. I've been poking around for five days now without seeing any issues.
Let's make sure the bug is gone, though! If you see a world with no mobs anywhere, post here ASAP and let me know the world name. Thanks, and good mob hunting!