I might be having a similar issue since MCPE 1.6 on an IOS device (iPad Air). When I am loading one of my worlds (world size 21.6 MB) the app appears to crash out. Sometimes I can play for a few seconds but usually the app shuts down before I can interact. I noticed that I am spawning near a part of the world where I have a lot of aquatic mobs like tropical fishes. In other worlds, I can play fine, but when I travel to an area where I had previously (prior to updating to 1.6.0) created a lot of aquatic mobs, then the app crashes. Then I can no longer play that world again since I am spawning in that “bad” part of my world.
I have been having a similar problem of crashing out of the Minecraft app on my iPad Air 2 (non-server world). This happens when I am loading one of my worlds and also in another world when I move to an area of many mobs. This happens on both MCPE 1.6.0 and 1.6.1.
I just tried something on the same iPad Air 2 to see if I could reproduce in a new world (MCPE 1.6.1). I created a new world in creative/peaceful mode. Built a 7 by 7 by 4 high glass tank. Filled it with water.then started adding Tropical Fish (via eggs). When adding the 35th fish the Minecraft PE app crashed. I was able to re-enter the world, but on adding an additional 6 Tropical Fish the app crashed again. Here is a summary of attempts:
Started new creative/peaceful world, built glass water tank, adding Tropical Fish to tank and on 35th fish app crashed
reopened world, adding more Tropical Fish to tank and on 6th fish app crashed
reopened world, adding more Tropical Fish to tank and on 6th fish app crashed
reopened world, adding more Tropical Fish to tank and on 10th fish app crashed
reopened world, adding more Tropical Fish to tank and on 3rd fish app crashed
reopened world, adding more Tropical Fish to tank and on 12th fish app crashed
reopened world, world starts to appear, then app crashed
reopened world, world appears for less than a second, then app crashed
The current size of the world is 0.34 MBs.