No easy way to reproduce this but the game will just randomly freeze and you need to go back to dashboard and quit the game and reload. This is only just started to happen in 1.6.0.8 as the game was fine in previous betas with no freezing. It has happened in the overworld and the nether and seems to be more likely to occur if you are traveling around rather than staying within the already loaded chunks. In one occurrence it froze shortly after i had re-spawned from dying whilst trying to fight the Wither and when I reloaded the game the items i had picked up after my death just before it froze had disappeared and so had the Wither, but the items i had not picked up were still on the ground. Not too fussed with the 2nd part as seems related to the freezing rather than another actual bug.
MCPE-36317
random freezing
Resolved
Invalid
1
Random crashes like this are automatically logged and sent to Mojang for further investigation and hopefully a fix, this means by simply playing the game you have helped find some issues. We have been asked to close tickets about random crashes as Invalid for this reason.