This might be the same issue as the falling sand on snow, but I don't know.
I put a piece of gravel on the side of a 3-block tall tower with a slab on the bottom.
And it fell like it should, but suddenly disappeared when it reached the slab.
The device is a Acer Iconia Tab A200.
Duplicate of MCPE-1682 . Please use the search function currently over 56% are closed by duplicate